Nuts And Volts

PROJECTS m THEORY @ APPLICATIONS ® CIRCUITS m TECHNOLOGY

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NUTSéVOLTS

pbs tageouiaacl EVERYTHING FOR ELECTRONICS

Ethernet Core Modules with

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The goal: Control, configure, or monitor The method: Create and deploy applications from The result: Access device from the

a device using Ethernet your Mac or Windows PC. Get hands-on familiarity Internet or a local area network (LAN)
with the NetBurner platform by studying, building,
and modifying source code examples.

The NetBurner Ethernet Core Module is a device containing

everything needed for design engineers to add network control NetBurner Development Kits are available
and to monitor a company's communications assets. For a very to customize any aspect of operation

low price point, this module solves the problem of including web pages, data filtering, or
network-enabling devices with 10/100 Ethernet, including custom network applications. The kits

those requiring digital, analog and serial control. include all the hardware and software you
need to build your embedded application.

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Telephone | 1-800-695-6828

Then take it out for a test ride while the sun sets. See it zip around, equipped with a sense of

sight, sound, smell, speed, heat or cold; or thunder detection, speech recognition... whatever
you imagine, there's probably a sensor or transceiver click” board that can do it (there's more
than a 100 available). Just plug one in to add a function. Zero hardware setup. And you choose
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DEVELOPMENT TOOLS I COMPILERS I BOOKS www.mikroe.com/buggy

April 2015

24 Build Your Own Arduino Barograph

Feeling pressure? Then, you need a barograph to
measure it!
@ By Mark McGuire

28 Build the Super KISS Timer

Ever built a project that needed an accurate timer to
switch something on or off at regular intervals?

See if this simple one fits the bill.

@ By Frank Muratore

32 Build the Annoy-0-Matic

You'll always be ready for April Fool’s Day with this
easy circuit that will help bring practical jokes to a
whole new level.

@ By Bob Diaz

38 Beyond the Arduino — Part 2

Last month, we established a hardware platform to
work on. This time, we'll dive right into working in a

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48 Add a Real Time Clock
to Your PIC Projects

RTCs have all kinds of neat uses in microcontroller
projects. Get introduced to this wonderful world of
timekeeping with the popular and inexpensive
TinyRTC.

lm By Thomas Henry

02 Driving LEDs with a Microcontroller

Typically, one of the first experiments people do
when working with microcontrollers is to blink an
LED. However, the thrill of this wears out pretty
quickly, so let’s see what else can be done.

i By Craig A. Lindley

Page 52

new environment.
@ By Andrew Retallack

08 TechKnowledgey 2015
Events, Advances, and News
The world’s largest digital camera has been funded,

Intel is getting sticky, you can get skin care via your
iPhone, plus there’s lots more to read about.

O3A
Reader Questions
Answered Here

Making a smart house smarter, a telephone
off-hook alarm, and radio tuning are question
topics this time.

The Spin Zone
Adventures in
Propeller Programming
Can We Talk? Again?

This month’s project goes through setting up a
simple command language for controlling the
Propeller through a serial interface.

Departments =

06 DEVELOPING 66 ELECTRO-NET

PERSPECTIVES
Amateur Radio — Not 74 NV WEBSTORE

Just for the Nostalgic 77 CLASSIFIEDS
07 READER FEEDBACK (78 TECH FORUM
_22 NEW PRODUCTS 81 AD INDEX

_23 SHOWCASE

U6 The Design Cycle
Advanced Techniques for
Design Engineers
The RN4020 PICtail Plus BLE.
Bluetooth 4.0 is becoming the de facto standard
when it comes to embedded device monitoring and
control from iPhones and Android devices.
Microchip’s BLE radio module is called the RN4020.
Unlike many of the other BLE offerings, the RN4020
Bluetooth Low Energy radio module comes backed
with a full load of example code and hardware
development tools. This month, we'll get started on
the BLE path with Microchip’s RN4020 P!Ctail,
a terminal emulator, and a laptop.

Practical 3D Printing
Real World Uses for the
Electronics Experimenter
3D Custom Storage Boxes.

Get your electronics tiber organized with specially
designed storage drawers.

Near Space

Approaching the Final Frontier
CubeSats — Part 3:

Attitude and Velocity.

Learn about some “toys” that help CubeSats control
their own attitude and velocity.

10

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4 NUTSZVOLTS April 2015

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DEVELOPING

i — — |

Amateur Radio — Not Just for the Nostalgic

hen | received my new catalog from MF) Enterprises, |

couldn't help but feel a twinge of nostalgia. Scanning
through the pages of the latest ham gear revealed very little
has changed since my youth. Sure, some of the instruments
sport LCD displays instead of analog meters or LED displays,
but from a gross technological perspective, the catalog could
have been from the ’70s. There was the usual mix of
antennas, antenna rotors, linear amplifiers, antenna tuners,
watt meters, microphones, and even a handful of iambic
keyers for CW operation using Morse Code.

It’s no secret that amateur radio has been in decline for a
while, hastened by the popularity of the Internet. It used to
be an accomplishment to chat with someone in Africa or
Japan. Plus, slow-scan TV was good for perhaps a frame
every couple seconds. Today, all that’s required for world-
wide video and audio communications is a cell phone — not
a room packed with powerful gear. | can remember
calibrating my wall clock and oscillator circuits with signals
from WWYV at 5.0 MHz and 10.0 MHz. Today, of course,
clocks with built-in receivers update the displayed time
automatically.

In short, most electronics enthusiasts don’t consider
amateur radio at the cusp of innovation in technology. And,

perhaps it isn’t. However, if you’re really serious about
learning and experiencing electronics, you owe it to yourself
to check out what amateur radio has to offer. | still use the
diagnostic techniques | learned building and troubleshooting
communications gear today — on both digital and analog
circuits.

I still remember my first moonbounce communications
using a microwave transceiver and an antenna array that
automatically tracked the moon. Of course, it took months to
prepare for what was about a minute of communications
time. There was learning about high gain antenna arrays, and
then using coat hangers and aluminum tubing to construct an
array. There was working with waveguide and heliax, and
figuring out the trajectory of the moon on a particular night.
Plus, there were a couple dozen other problems that had to
be solved. As a result, | learned a lot with each project. At
least for me, it isn’t about the final conversation, it’s the
process of building a system with specific capabilities and
then operating it to the best of my ability.

You won't find that sort of challenge or excitement
working on a bench with, say, a microcontroller and a few
LEDs. It’s one thing to build a power supply to use one day
on your projects, and another to build one specifically to
power a transceiver that has to stand

Feedback Motion Control

The Old Way

1) Build robot

2) Guess PID coefficients
3) Test

3a) Express disappointment
3b) Search Internet, modify PID values
3c) Read book, modify PID coefficients again
3d) Decide performance is good enough

3e) Realize it isn’t

31) See if anyone just sells a giant servo

3g) Express disappointment

1) Build robot
2) Press Autotune
3) Get a snack

3h) Re-guess PID coefficients Kangaroo x2

34) Switch processor

3}) Dust off old Differential Equations book adds self-tuning

3k) Remember why the book was so dusty

3) Calculate new, wildly different PID coefficients feedback to SyRen

3m) lewent new, wildly different swear woeds Sabertooth

Bn) Research fuzzy logic and motor
3a) Now it is certainty mot working in umcertaim ways drivers.

Bp) Pull hale

34) Sweltch comrotter

Sr) Re-guess PID cowllicients

Se) Switch progeannining language

34) Start a mew project that doese’t need feedback control
lit) See parts te bow. Feel guilty. Ge back te ofl project

Iv) Mart levting every posible combination of PD cortictents
dhs) Apply epe drops to red, bileary, sleep-deprived eyes

15) Wat, it's workingt

4y) Deckle nat todo say mace progects tut reqsie contre’ systmane
Az} Wonder why someane doesn't just make 2 thing that tunes iteelf

6 NUTS2VOLTS April 2015

The Kangaroo kz

up to the rigors of emergency use.
Amateur radio has a long history of
public service. | spent many hurricane
seasons in Louisiana providing
communications for hundreds of
families in temporary shelters. That’s
when knowing how to set up an
antenna with duct tape and coat
hangers paid off — not only for me, but
for everyone in the shelters.

In future issues of Nuts & Volts,
we’re going to feature articles targeting
the amateur radio community. If you’re
new to amateur radio, | invite you to at
least skim the articles. | think you'll like
what you find. If you happen to be a
seasoned ham, then please consider
contributing an article for your fellow
Nuts & Volts readers.

$24.99 DimensionEngineering NUIN NV

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NUTS VOLTS

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READER F

Im-PART-ing Knowledge

| was wondering where J.W.
Koebel gets his replacement parts
from for his radio repairs.

Lee Gernes

| generally use Mouser.com for
my parts since they have a huge
selection and really granular search
options. It's not always the friendliest
site for a hobbyist to order from,
though.

NTE PartsDirect
(www.ntepartsdirect.com) has a
good selection as well, and their
passive components like capacitors
and such are marked by common
voltages. Plus, it's pretty easy to
navigate.

There are a few other smaller
suppliers catering to the hobbyist
radio repair market. Just Radios

(www.justradios.com) or Sal's

Antique Radios
(www.tuberadios.com) carry
commonly needed sizes for vintage
radio repair. Since they're very
focused, you don't have to wade
through a ton of options to find what
you're looking for.

| generally purchase tubes from
Antique Electronics Supply
(www.tubesandmore.com) as they
have new and good used tubes at
pretty reasonable prices for most
types.

If | need controls or switches
rebuilt, | generally use Antique
Audio/Mark Oppat's Old Radio Parts
(www.oldradioparts.net). He's an
expert in controls who can rebuild or
custom build nearly any value of
control.

Continued on page 80_

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April 2015 NUTS&VOLTS 7

TECHKNOWLEDGEY 2015

m@ BY JEFF ECKERT

ADVANCED TECHNOLOGY

M Artist's rendering of the LSST camera.

World's Largest Digital Camera Funded

f you are in the market for a great pro-level digital camera, you

might take a look at the Nikon D4: a 16.2 MP unit that lists for
$5,999.99 (plus lenses). It's pretty impressive, but how about a
3,200 MP camera — the final cost of which has been estimated
at about $167 million? We're talking about the centerpiece of
the Large Synoptic Survey Telescope (LSST) which recently
received key "Critical Decision 2" approval from the US
Department of Energy. The camera — scheduled to be in
operation atop a mountain in Cerro Pachén, Chile, by 2022 —
will be the size of a small car and weigh more than three tons.

Operated by the DOE's Stanford Linear Accelerator Center
(SLAC) and National Accelerator Laboratory
(wwwe6.slac.stanford.edu), it is designed to help researchers
study galaxy formation, track hazardous asteroids, grab a look at
exploding stars, and gain a better understanding of enigmatic
dark matter and dark energy which together make up 95
percent of the universe. According to SLAC, it will produce the
widest, deepest, and fastest views of the night sky ever
observed. Over a ten year period, the observatory will detect
tens of billions of objects and create movies of the sky with
unprecedented details.

"The telescope is a key part of the long-term strategy to
study dark energy and other scientific topics in the United States
and elsewhere," said David MacFarlane, SLAC's director of
particle physics and astrophysics. "SLAC places high priority on
the successful development and construction of the LSST
camera and is very pleased that the project has achieved this
major approval milestone."

Components of the camera will be built by an international
collaboration of labs and universities, including DOE's
Brookhaven National Lab, Lawrence Livermore National Lab,
and SLAC itself, where the camera will be assembled and tested.
A

8 NUTS2VOLTS April 2015

Levitation Made Simple

eee has long been a staple concept for folks,
ranging from Hindu gurus to magicians. It is a
pretty difficult thing to achieve outside the world of
illusion and fakery, but there are a few real methods
including magnetic and acoustic levitation — the latter
of which is used for "containerless processing" of
various materials. It involves suspending an object
between a sound source and a reflector using the
reflected acoustic waves.

Until recently, this has required a very precise
setup in which the source and reflector had to be
located at fixed resonant distances, which makes it
difficult to control the levitated objects. However,
researchers with the University of Sao Paulo
(www5.usp.br) have devised an instrument that can
make a small object hover while exercising much
greater control over it.

The instrument demonstrates that it is possible to
build a practical nonresonant device, i.e., one that
does not require a fixed separation between the two
main components. Moreover, it shows that levitation
can do more than just trap objects in a fixed position;
it can also transport them through short distances in
space. According to Marco Aurélio Brizzotti Andrade,
who led the research, "Modern factories have
hundreds of robots to move parts from one place to
another. Why not try to do the same without
touching the parts to be transported?"

Unfortunately, his levitator can lift only very light
objects at this point; it was tested with 3 mm blobs of
polystyrene. "The next step is to improve the device
to levitate heavier materials," Andrade noted. A

Hf Ultrasonic emitter (top) and reflector
(bottom) suspend polystyrene blobs in
acoustic standing waves.

EVENTS, ADVANCES, AND NEWS

COMPUTERS and NETWORKING

Intel Gets Sticky

t may look like an Amazon Fire TV Stick or a similar

streaming device, but the Compute Stick from Intel
(www.intel.com) is actually a real live computer that
comes with your choice of Windows 8.1 or Linux
preinstalled. Powered by a quad-core Atom Z3735F
processor, the Windows version also features built-in
802.11bgn Wi-Fi and Bluetooth 4.0, 2 GB of RAM, 32 GB
of storage, a microSD slot, and a USB 2.0 port — all for
$149.

If even that doesn't fit your budget, you can opt for
the Ubuntu Linux version which goes for $89, but you
only get 1 GB of RAM and 8 GB of storage.

Either way, just connect it to the HDMI and USB (for
power) ports of your TV set, hook up a USB or Bluetooth
keyboard, and you're ready to run your favorite
applications. And, of course, you can also stream Nettlix,
Hulu, or games. A

Bi Intel's Compute Stick,
the world's smallest
Windows computer.

3D Printer with Autodesk Models

f you've been thinking about getting a 3D printer but have

been reluctant to buy one from a company that operates out
of a garage in Podunk, maybe the name Dremel
(www.dremel.com) will instill some confidence. Billed as the
most user-friendly unit on the market, the 3D Idea Builder is
designed to inspire and empower the end-user to build on
their own ideas with the support and mentorship of the
Dremel experts. The company, in partnership with Autodesk,
provides free print-ready models and design tools with the
unit, and offers a flow of new design tools on dremel3d.com.

The machine features a color touch screen and onboard

print software, plus, the work area (9 x 5.9 x 5.5 in) is fully
enclosed to reduce noise. A cooling fan prevents warping of
the workpiece, and the print head provides 100 micron
resolution and a choice of 10 colors of PLA filament. You can
pick one up at Home Depot or order one online, but it will
set you back a fairly substantial $999. A

@ Dremel's 3D Idea Builder printer.

April 2015 NUTS2VOLTS 9

/article/april2015_TechKnow15.

CIRCUITS and DEVICES

USB 3.1 Type C Arrives

n case you haven't heard, USB connectors have

been majorly redesigned. The new Type C
connector showed up at the International
Consumer Electronics Show back in January with
pretty much universal acclaim. For one thing,
both ends can be identical — unlike a micro USB
— so you can plug either end into a compliant
camera, computer, or whatever. Another nice

USB 3.1
Standard-A

Post comments on this article at www.nutsvolts.com/index.php?/magazine

Hi Comparison of
USB connectors.

Micro-B

feature is that it is reversible, so you won't end up trying to plug it in upside-down on the first attempt.
In addition, it is compatible with USB 3.1, which operates at up to 10 Gbps and can deliver up to
100W of power. The only problem, of course, is that you probably don't have anything that can use it

yet. For details, visit www.usb.org. A

Skin Care via Your iPhone

s your skin itchy, broken out, or infested with a rash that

won't go away? Do you have painful boils or pustules
that cause other people to make retching sounds? Well,
you're in luck, because Oku (getoku.com) is here. Said to

nanotechnology, and spectroscopy (no details are offered
as of this writing), Oku is an iPhone dongle devoted
specifically to examining and maintaining the wellness of
human skin. All you have to do is connect it, download
the app, and let it do the rest.

According to the website, "Oku sees what you can't
— by literally looking under your skin. It takes a scan of
your skin, analyzes it in detail, takes into account your
lifestyle information, and provides you with an easy to
understand value called the SkinScore. This will tell you
how your skin is faring and identifies areas for
improvement. It then sets a daily goal towards unlocking
the youthful best of your skin. Oku gives advice on your
lifestyle and diet, and will recommend the right products
for your current issue, or the right routine to improve
your skin wellness." The bad news is that it will run you
$299 unless this gets to you before the $249.95 preorder
offer runs out. A

be based on a combination of dermoscopy,

The Oku skin care
dongle for the
iPhone.

Wi-Fi Range Booster

f you're tired of losing your Wi-Fi signal every time you go out

to the mailbox or down into the basement, the solution might
be the new TAP-EX2 touch screen range extender (also referred
to as the model AC750) from Amped Wireless
(www.ampedwireless.com). Designed to work with any Wi-Fi
network, it eliminates many dead spots and provides faster
802.11ac connections. Using six amplifiers and two high-gain
antennas, the 800 mW unit is said to provide as much as
10,000 ft? of extended coverage. The touch screen is used to
control all functions, including setup and management of guest
networks, access scheduling, user access controls for Wi-Fi
strength, and other parameters. Notably, the unit was chosen as
a 2015 CES Innovations Design and Engineering Awards
Honoree at the Las Vegas show. The EX2 was introduced at the
show, but no MSRP was revealed. The previous model, however,
was priced at about $120. A

Mi The new TAP-EX2 Wi-Fi
extender from Amped Wireless.

10 NUTSVOLTS April 2015

CIRCUITS and DEVICES continuea

Outpeep the Peepers

f course you are not involved in any illegal, immoral, or

otherwise embarrassing activities that you don't want
anyone to know about. Certainly not. But if you were, you
might be alarmed to know that several companies manufacture
optical devices that let police or other snoopy people reverse
the function of door peepholes and see (and even photograph)
exactly what's going on inside.

However, for every tactic, there is a counter-tactic. So, if
indeed there is something fishy going on (or you're just
paranoid), check out the Brinno (www.brinno.com)
PHV132512 Digital PeepHole Viewer.

Not only does it prevent visitors from spying on you, it turns The Brinno PeepHole Viewer ensures privacy.
the peephole image into a big bright digital image on the unit's
display. It also compensates for low-light conditions and
eliminates fisheye distortion.

To conserve battery life, the viewer automatically shuts
down after 10 seconds. It installs easily in doors from 1.375 to
2.25 inches thick, and the two AA batteries are included. It lists
for $129.99, but scrounging around the Internet turned up
prices as low as $89.95. A small price to pay if you and Agnes
(the goat) need a little privacy. A |

INDUSTRY and the PROFESSION
Computer Hits Age 60

ost of us are aware of the Electronic Numerical Integrator And Computer (ENIAC) which became the first
IN eaten general-purpose computer in 1946. Fewer are familiar with the Weizmann Automatic
Computer (WEIZAC) which debuted 60 years ago. Based on the Institute for Advanced Study (IAS) architecture
created by John von Neumann, it was Israel's first computer and one of the world's first large-scale, stored-
program machines in the world. The machine operated on
40-bit words and used punched tape for I/O (later, magnetic
tape). Memory consisted of a magnetic drum that could
hold 1,024 words (later expanded to 4,096).

The program to develop WEIZAC was initiated by Prof.
Chaim L. Pekeris, who wanted to use it to solve Laplace's
tidal equations for the Earth's oceans and other tasks,
including defense-related ones. Eventually, it was also used
for earthquake studies, atomic spectroscopy, numerical
analysis, and so on.

Interestingly, although von Neumann supported the
project, fellow Applied Mathematics Department committee
member, Albert Einstein thought it was a bad idea. WEIZAC
was fired up in 1955 and operated through 1963. In 2006, it
was recognized by the IEEE as a milestone in electrical

engineering, and the team who put it together was awarded .
the "WEIZAC Medal." NV W Israel's first computer, the WEIZAC.

April 2015 NUTS2VOLTS 11

WITH TIM BROWN

O&A

In this column, Tim answers questions about
all aspects of electronics, including computer
hardware, software, circuits, electronic theory,
troubleshooting, and anything else of interest to
the hobbyist. Feel free to participate with your
questions, comments, or suggestions. Send all

questions and comments to: QGA@nutsvolts.com.

¢ Making a "Smart House"
Even Smarter

¢ Telephone Off-Hook Alarm
¢ Radio Tuning

Post comments on this article at www.nutsvolts.

com/index.php?/magazine/article/april2015_OA.

Making a "Smart House" Even Smarter

Whenever | see a version of "smart house"
advertised, | check to see if it has what | need,
and it never does. | want something that will tell
me when my microwave oven stops, when my
dryer stops, and when my washer stops — without
modifying the appliances themselves. I've made little
boxes to plug microwaves and dryers into, and they let me
know when these finish, but the washer eludes me.
Sometimes the motor is taking a lot of current, but
then in the next second, all that's running is the timer to
get to the next action. | know that a GFCI handles a lot of
current while detecting a small amount of current; is there
a way to change this circuit to tell me when the washer is
completely finished?
— John Harris
Anaheim, CA

The automatic clothes washing machine was a
real boon to laundry day because it did not have
to be constantly attended (contrast with the
wringer type machine, rub board and wash pot,
or creek and rock methods). In the 1950s, my mother
bought a wringer type washer and though it was fun to
watch, it was a pain to use (literally at times, when she

Start Timer starts moving to initiate the cycles (timer energized —
very low current)

Fill Water solenoids open and fill tub to desired level (solenoid on
— low current)

Wash Agitator operates to slosh dirty clothes (motor on — high
current)

fain Pump operates to remove water from tub (motor on — high
current)

Fill Water solenoids open and fill tub to desired level (solenoid on
— low current)

Agitator operates to slosh clothes to remove detergent

Binge (motor on - high current)

Tub spins to remove water from clothes to aid in drying

Spin (motor on — high current)

Off Timer stops moving (timer de-energized — no current on most
machines, | would think)

ees

12 NUTSZVOLTS April 2015

fablet.

caught her hand in the wringer). Modern washing
machines perform the wash cycle without human
intervention and some even weigh the contents of the tub
to determine how much water, detergent, bleach, etc., to
use. My washer has a signal that sounds at the end of the
operating cycle. Most automatic washing machines have a
sequence of cycles controlled by a timer that is roughly
the same as what’s shown in Table 1.

As you can see from the washing machine cycles, the
current to the machine varies greatly throughout the
operating sequence. So, using current measurements to
determine when the cycle is finished is not a viable option
(microwaves and dryers only turn ON and OFF once
during a standard operation). My washer has a signal
which is activated by a contact on the timer, but if you do
not have a signal already, your timer most likely will not
have this contact. (Caution: Unplug the washer before
opening the control box. This is the easiest option, so
check the timer schematic to be sure).

One idea | have — if you want to use a "box" that
plugs between the receptacle and washer plug — is to use
a current transformer around one wire going to the
machine [see "Measuring Current with Clamp-On
Ammeter"/Q&A October 2014 for more info]. If the signal
is too small, use a pre-amp. Use a full-wave bridge rectifier
to convert the AC to DC, and a Schmitt trigger to square
the waveforms. Count the number of current (or voltage)
cycles with a pre-settable digital counter and turn in a 555
one-shot to activate a piezo buzzer for a short time (my
washer has eight or nine operations per cycle, depending
on if you select extra rinse or not) when the counter pre-
set is reached. Be sure to isolate the digital electronics
from the 110V AC power. The GCFI only detects a
mismatch in current between the hot and neutral leads
such as when one of the leads is grounded and the other
is not. In normal operation, the GCFI does not give any
indication that would be useful in your indicator [see
"Testing GCFls Properly" Q&A January 2015 for more info].

Since most dryers and microwave ovens have built-in
buzzers to indicate the cycle is finished, | think you may
be looking for a visual indication so you could substitute
an LED (with proper current-limiting resistance) for the
piezo buzzer. An illuminated LED would let a hearing
impaired person know when the washer was finished if

QUESTIONS and ANSWERS

they were in the vicinity of the machine, of course.

In my case, the washer cycles in 30 minutes versus 60
for the dryer. So, once the first load is put into the dryer, |
don't need to know when the washer cycle is over (most
of the time). As one of my idiosyncrasies, from the den |
can tell when the washer finishes because it makes a
unique "clunk" only at the end of the cycle.

Your mention of a "smart house" reminds me of the
magazine articles that spend many pages touting the
marvels of a smart home, such as when you can have the
coffee maker prepare your morning coffee while you
sleep or turn the oven on to cook a roast for dinner.
However, someone has to put the roast into the oven, or
put coffee and water into the coffee maker.

My philosophy is that people are getting too lazy and
need some kind of daily physical activity (besides a gym
visit) to keep their bodies working as they should. |
remember an EE professor in the early ‘70s talking about
the "recent" developments in computer-aided circuit
design. He said, "This may be an example of a technology
that destroys the fundamentals that created it." Technology
is great, but many things in our lives need a human touch.

Let me know how this idea works.

Telephone Off-Hook Alarm

Some of us who still have land lines for one
reason or another (security system, etc.)
sometimes leave a phone off-hook. How about a
system to remind you that the off-hook situation
exists? Since no audio is on the line (just off-hook voltage),
the off-hook warning has to trigger on voltage only, no
signal. A pause in conversation has to be considered, and
the warning/alert needs to last until it’s shut off by the
occupant. The off-hook voltage varies between different
carriers; the off-hook voltage for the privately owned
carrier | have is approximately 13.0 volts. AT&T is
approximately 8.6 volts.
— Robert
via e-mail

Land line telephone systems operate with an on-
hook voltage of approximately 48 VDC, an off-
hook voltage of 3 to 9 VDC with a current draw
of 15 to 20 milliamps, and a ringing voltage of
90 VRMS AC at 20 Hz (these values vary somewhat
between phone companies and distance from the central
office). When the phone is off-hook and idle for a length
of time determined by the phone company, the phone
system will send out an obnoxious tone and a message to
alert the user that they have left the phone handset off the
hook, thus rendering the phone useless.
In the North American Numbering Plan, a quad-
frequency tone is used consisting of frequencies 1,400 Hz,
2,060 Hz, 2,450 Hz, and 2,600 Hz, with a duty cycle of

50 percent (0.15 on, 0.1s off). If | were to design an off-
hook alarm device, | would use the phone company's
alarm (the hard work has already been done, so let's use
their signal) and | would use a high pass filter with a cutoff
frequency of 200 Hz to eliminate the ringer signal, but
pass the off-hook signal from the phone company
(including those that still use the old GTE 480 Hz alarm).
This filter would feed either an audio amp circuit (if you
want an audio alert) or a full bridge rectifier/capacitor
circuit feeding an LED for a visual circuit or a PIC detector
(if you are into programming).

Fortunately, this circuit has already been incorporated
into commercially-available devices such as the Serene
Innovation HD-60 at $100+. The HD-60 is pricy but it is
ready to go out of the box, hearing impaired compatible,
and approved for use with telephone systems. Most
telephone providers are extremely adverse to customers
installing unapproved devices on their systems without
proper isolation (a.k.a., unapproved equipment). This
sounds like a draconian measure, but it is designed to
protect the technicians working on the line from
electrocution (the power company has similar restrictions
for customer devices connected to their power grid).

| found several cheaper indictors, but they all
illuminate all of the time the phone is off-hook, so they do
not meet your requirements to activate when the line has
not been used for a period of time.

Let me know if this satisfies your needs.

Radio Tuning

| have a small transistor from which | can only
receive static. | opened the radio up and noticed
there are several square "cans" that have a
slotted screw on the top. Will turning one of
these screws allow the radio to receive AM stations again?
— Barbara Weathers
Kissimmee, FL

| remember my first pocket-sized transistor radio
from the early ‘60s. | was a teenager, and the
tiny black radio only received the AM
(Amplitude Modulated) band (for you
youngsters, this is the band you don't use on the AM/FM
radio) and had to be positioned properly to receive a
signal well. This radio was great because it was portable
since it was powered by a single nine volt battery (which |
still call a transistor radio battery). The other radios of the
day were desk or table models which plugged into the
house power receptacle, so the transistor radio was a truly
mobile device. | was reading everything | could about
radio and television electronics at the time, so | naturally
opened up the radio one day and admired all of the neat
tiny electronic components.
Desktop radios were loaded with tubes/sockets, huge
resistors/capacitors, and point-to-point wiring. They were

April 2015 NUTSEVOLTS 13

easy to fix by replacing a tube, but not too mobile unless
you had a very long extension cord. Plus, they weighed
more than the latter day boom boxes. (I'm not old like it
seems. | just hav8e lots of experience.) Naturally, my
attention was attracted to the square silver "cans" with the
brightly colored slotted screws, but | soon learned to
NEVER turn one of those screws if you ever wanted the
radio to work again.

The AM radio detects radio frequency signals (RF)
from 540 to 1,600 kHz by mixing this input signal from
the antenna tuned circuit (sometimes one of the "cans")
with a local oscillator circuit (another possibility for the
cans) to produce an intermediate frequency signal (IF) at
455 kHz which was more efficient to amplify the RF
signal. The other two cans were used to tune the two
stages of circuits that fed the IF into the rest of the radio.

The tuning is essential to creating a narrow band filter
at the correct resonant frequency which eliminates
extraneous signals created by the heterodyning process or
spurious RF channels. Interestingly enough, the
demodulator for the AM signal could be a diode (FM
demodulation is a LOT more involved). Tuned is the key
word to why you NEVER touch the screws on these cans
(really they are variable transformers with movable ferrite

slugs). The RF and IF transformers (and sometimes the
local oscillator) are used to adjust the coupling between
the primary and secondary windings and thus the width of
the passband (greater coupling gives wider and flatter
passband; the capacitor sets the center frequency of the
filter passband). So, if you ham-fistedly turn a screw, you
now are operating with a non-optimum passband. You will
either not hear the radio station's broadcast (this is the
voice of experience) or there will be excessive noise.

To correct this problem, you need a circuit schematic
(to find the correct test points), an RF/IF signal generator
to input a known signal (I happen to have some ‘60s
vintage military surplus generators), and a voltmeter,
speaker, or oscilloscope to verify when the maximum
output is reached from the IF and RF/LO circuits. The high
end receivers have a manual that specifies the passband
needed for best operation.

Most transistor radio problems are related to the
transistors, diodes, resistors, capacitors, fixed inductors
(coils and transformers), or the circuit board. | once fixed a
squealing problem by touching each resistor with a pencil
eraser until the problem stopped — revealing a cracked
resistor which could not be seen with my (then) youthful
naked eye. | hope this answers your question. NV

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April 2015 NUTS2VOLTS 15

lm BY JON MCPHALEN

THE SPIN ZONE

Can We Talk? Again?

as friendly as my memory led me to believe. A friend

of Lon's actually deployed HFCP but has since moved
on, leaving Lon and me to sort things out. In addition to
this, another project we're working on together requires
configuration files on an SD card attached to the
Propeller. HFCP is designed for command and control, not
processing text from files. | needed a new tool.

What | created is a generic parsing engine; one that |
could use on-the-fly for command and control, and one
that | could pass complete strings to that might be built
into a program or are read from a file (that was actually
very easy). Like HFCP, everything is text based. We can
use a simple terminal to communicate commands to a
project, and the responses can be as verbose as we like.
Again, it's plain text. For projects with an SD card
attached, we can open and process text files.

Every coin has two sides, and the other side here is
that the easier we want to make the interactions for
humans, the more work we have to do in the code. This
month's project goes through setting up a simple
command language (we're going to use PBASIC-like
commands) for controlling the Propeller through a serial
interface.

16 NUTSZVOLTS April 2015

Te not to say that HFCP is bad. It isn't — it's just not

Ready ... Set ... Action!

Let's jump right in, shall we? In a live application, we're
going to accept a character from a serial stream and pass
it to the parser.enqueue() method. This method will store
the incoming character in a string buffer; when a line
terminator (CR, LF, or 0) is detected, the string will be
parsed. When this happens and tokens are available, the
parser.enqueue() method returns true.

In an application, we'll usually see something like this:

As you Can see, we're waiting on a character from a
serial stream. When that arrives, it gets passed to the
parser. When tokens are ready (result is true), we call
process_cmd and then reset the parser for the next
command. Mind you, the serial data can come from
anywhere; our demo code will use the programming port,
but it could just as easily be coming from an $8 Bluetooth
device running SPP mode. I've been doing that and it's a
lot of fun.

For clarity, when I use the term 'token' | am referring
to a group of valid characters. Any other characters are
not valid; hence, used as separators. This allows us, for
example, to parse values out of a CSV (comma-delimited
text) file that might use a comma and space between
fields. The point is we don't have to define special
separator characters; anything not valid is taken to be a
field separator. This string:

HIGH 26<CR>

has two tokens: 'HIGH!' and '26.' The space character is
not part of the valid set, so is used as a separator.

How does the parser know what's valid and what's
not? We tell it, of course, using its parser.start() method
which looks like this when implemented:

The parser.start() method takes four parameters: 1) a
pointer to a string that defines the valid character set for
the application; 2) a pointer to a list of tokens used by the

ADVENTURES IN PROPELLER PROGRAMMING

Post comments on this article and find any associated files and/or downloads at

www.nutsvolts.com/index.php?/magazine/article/april2015_SpinZone.

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Propeller Activity Board Parallax #32910

Bluetooth (RN-42) Parallax #30086

Bluetooth (RN-42, Xbee style) SparkFun #WRL-11601

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application; 3) the number of tokens the application can
use; and 4) a true or false value that sets case sensitivity.
In most applications, we will use false which causes the
parser to convert everything to uppercase — this simplifies
command processing.

The valid characters and token strings are defined in a
DAT table:

dat
CHAR_SET byte Sede 0
byte UOLZ SADE ey
byte "ABCDEFGHIJKLM"
byte "NOPQRSTUVWXYZ"
byte 0
TOKEN LIST
TOKEN HIGH byte WisGGia (0)
TOKEN LOW byte "Low", O
TOKEN_ON byte ONO.
TOKEN OFF byte womet, 0)
TOKEN FREQ byte "FREQOUT", O
TOKEN BLINK byte Wise ION, (0)

The character set is a contiguous string, even if broken
across multiple lines. The only place we find the 0
terminator is at the very end. The list of tokens on the
other end is a set of individual strings. | add in a label
called TOKEN_LIST so that | can rearrange tokens as |
choose without having to update the call to the
parser.start() method.

In practice, | tend to order the list by expected use;
that is, tokens that are used frequently are at the top of
the list. This reduces search time for popular tokens.

You may be wondering about words versus numbers.
Yes, the character set we're using allows both words and
numbers.

In fact, beyond numbers and letters, the only other
valid characters we have in this program support Parallax-
style numeric formatting. The parser will evaluate 26, $1A,
and %1_1010 the same way.

We can use parser.token_is_number() to determine if
a token is a number, and if it is, use parser.token_value()
to convert it from text to a number. More on this later.

Under the Hood

Okay, let's have a look on the inside to see how this
works. The front end of the parser is the parser.enqueue()
method that accepts characters until an end-of-string
character is detected.

As | want to be able to use this for live control from a
terminal, it supports backspace (8) as well:

The parser.enqueue() method builds a string that is
stored in a byte array called queue. The position index of
the next available character is saved in gidx. When the
new character is any of the terminators, it is changed to 0;
the string is converted to uppercase if the csensitive flag is
false; and the possible tokens in the string are counted. If
the token count is greater than zero, they get extracted
and we return true to the caller. If we had a bad string
and there are no tokens, the parser resets itself and returns
false.

For live control, | thought the input should be human
friendly (there's that term again!) and support the
backspace character so mistakes can be dealt with. If
backspace (8) is entered and the buffer is holding
characters (gidx is greater than zero), we back up the
index and clear the last entry.

With any other character, we add it to the buffer — so
long as there is space left. I've made the buffer size about
twice as long as | think | need; this should prevent

April 2015 NUTS2VOLTS 17

Jon "JonnyMac" McPhalen
jon@jonmephalen.com

Parallax, Inc.
Propeller boards, chips,
and programming tools

www.parallax.com

RESOURCES

bumping into the end.

To this point, we've accepted any character into the
raw string. Counting tokens requires the use of the valid
character set and it's pretty easy. We're going to iterate
through the buffer; when we go from an invalid
(separator) character to one in the valid set, the token
count is incremented:

joule; Coline IeOlsssaus((e) fice) || Ol, iwisllee,
toks := 0
tflag := false

WEOSENE SGiceSiVe (9 Sie)
B= Jonata. Sera l|
ii (Stee 5 CiMsicw (jo Welles, ©) => 0)
if (tflag == false)
tflag := true
erates)
else
tflag := false

return toks <# N_ TOKENS

As you can see, it's a short method, taking advantage
of the str.cinstr() method from the strings object. The
return value is limited to the storage space for tokens; the
default setting is 10.

Let's say we have some tokens — time to parse them
from the string. At the heart of the process is
parser.extract_token() which looks a bit gnarly, but is
really not too bad:

joble) Grxciccloiwe clei Sai(Ge) Scie; ieakel<) || i
jj wesegeie, ieee, @, jewels, telleia

if (tidx => N_TOKENS)

rei urea
else

target := tidx
tflag := false

EEOSEIE SicESive(S_ See)
18 NUTSEVOLTS April 2015

G@ B= lIsyrce lia siete ||
aie (steie .alimsicie (Dwele, ©) < (0)
tflag := false
else
if (tflag == false)
tflag := true
if (target > 0)
=Sicehoo(c.
else
pltok ;= token addr (tid)
bytefill(p_tok, 0, TOK SIZE)
byte [omeoki |=.
tlen := 1
repeat
© g= lovee lio Sitesi]
aie (((Siteie c(eubialsheie (jer \elnicuesi, 6) = (0)
abe ((sraPicileiny << MONS (SiLZalm))
ISKAES TS Oke || 8= We!
else

rae eam
else
TAS EVEIAy

Again, the process is simpler than the code looks.
What we're going to do is iterate through the buffer until
we locate the target token (specified in tidx). Once that's
located, the storage space for that token (provided by
parser.token_addr()) is cleared, and the characters in the
string which make up the token are copied to the token
buffer. As expected, any non-valid character ends the
process.

It's logical to wonder why | didn't merge counting and
parsing tokens into a single method. | may, in fact, do that
later, but at the moment | want the flexibility to skip
parsing tokens if the count does not match what an
application is expecting (currently, parsing is automatic on
detection of a string terminator).

By Your Command

Okay, that's enough of the black box stuff. Let's put
this dude to use. The demo program allows us to give a
few PBASIC-like commands to the Propeller. The keywords
understood by the program are:

HIGH
LOW

ON

OFF
FREQOUT
BLINK

This is where it gets fun: We get to decide the syntax
rules for our commands. We've added ON and OFF which
work the same as HIGH and LOW, and we're going to

supplement the syntax rules so that we can use them like
PBASIC:

HIGH 26
Or, as "regular people" might prefer:
26 OFF

To be honest, | probably wouldn't have considered the
second syntax variation, but something interesting
happened while in a friend's shop a few weeks ago. He's
working on a scoreboard for a baseball park and asked
me about controls. During our conversation he very
casually stated, "I’d love to tell it something like, '3 balls'
and have the scoreboard update." This was a great piece
of information from a possible user.

| stated earlier that the easier we make things on the
outside (the human interface), the more work we have to
do on the inside. Believe me, it's worth the effort.

In the parser demo, a method called process_cmd is
called when parser.enqueue() or parser.enqueue_str()
return true:

pub process cmd | tidx
if (parser.token_is number (0) )

SDiKOCISS\_jSalia
DIEwEIA

ida parser dete tOkonmncl(paieser
token_addr (0) )

case tidx

T HIGH, T_ON
T LOW, T OFF
T_FREQ

T BLINK

set_pin(true)
Sisie_joulial (eel siS))
jSuliai_ipicteve)

: blink pin

As you can see, there's not very much to it; this
method is taking the first token and directing us to the
appropriate handler for it. At the very top, we check to
see if the first token is a [pin] number; if that's the case,
we call the process_pin() method and then return to the
main loop.

If the first token is a word, we use the
parser.get_token_id() method to convert the token string
into a numeric index that can be used in a case statement.
To simplify the case structure, | create an enumerated
constants list like this:

con

#0, T HIGH, T_LOW, T_ON, T_OFF, T_FREQ,
T BLINK

TOKEN COUNT = T_BLINK+1

For the moment, let's start with processing a very
simple command like HIGH 26 which will turn on the LED
on P26 of the Propeller Activity board. The index value to
the "HIGH" token is 0; hence, the case statement will call
a handler method called set_pin():

oul) Sere join (Sess) | joa

ime (jSelesicien Olden (coulme <> 2))
return

ee (Parser. toOkentecmmumls cre (l%)))

pan = parser. token value (i)
ifnot ((pin => 0) and (pin =< 27))
mere uaen!
else
Tee ile ial
outa[pin] := state

ll
es

dira[pin]

In all of my handlers, the first thing | do is verify that
the token count for the command is correct. For HIGH,
LOW, ON, and OFF, we should have two tokens, and the
second token must be a number. The pin number is
extracted using the parser.token_value() method, and
qualified for the available pins in the application. | only
allow PO through P27. This protects the ’C and
programming/debug pins. If everything checks out, we
write state to the pin and make it an output.

Want to have some fun? Update the set_pin() method
to work with two or three tokens. When three tokens are
used, the second and third tokens specify the boundaries
of a group of pins to make high or low.

Here's one approach: If the token count for set_pin()
is not two, call another method before returning to the
main loop. | called that method set_pins():

joibls) Siac jostine (SigeteS)) || wey, slo; miso

Tee (Parser. toOkenmcoun ts <3)
return

ine ((eelesieue e@ldeial a's) _iniuiloesie (11) |

mse parser rOkchm valwel())
ifnot ((msb => 0) and (msb =< 27))
1eSNE ILE Ig
else
met uTem

ie ((QebesiSe ieOlISial_sLs\_jalwlaloyssic (2) )

Isis) 2S jecwesiie, wolscia welluey (2)
apa ((ilsis) =s 10) euscl (isin =< 27))))

April 2015 NUTS2VOLTS 19

:
@ Parallax Serial Terminal - (COM12)

?

HIGH 26

-— length: 7

-- tokens: 2

—— token0: <HIGH>, string, id = 0
-- tokeni: <26>, number, val = 26

Cmd> 26 OFF
-- length: 6
—- tokens: 2
-- token0: <26>, number, val = 26
—-— tokenl: <OFF>, string, id = 3

Cmd> BLINK 26 5 i100 400
~- length: 18
—— tokens: 5
-- token0: <BLINK>, string, id = 4
-— tokeni: <26>, number, val = 26

—-— token2: <5>, number, val = 5
-— token3: <100>, number, val = i100
—— token4: <400>, number, val = 400

@ FIGURE 1. Parser report.

@ FIGURE 2. Android command app.

to blink at a 10 Hz rate until we stop it by
setting the frequency to 0.

Remember that counters work
independently and in parallel to the
normal pin output bits, so setting a pin to LOW or OFF
will not stop an active counter attached to it.

Here's the code that processes the FREQOUT

Kia
Corn Pout BaudRae @ TX [ DIR [ RTS i
[com12 7) }115200 ~ @ RX @ DSR @ CIS T EchoOn
Prefs Clear Pause Disable
return
else
Tee wEIM
command:

outa[msb..lsb] := state
dira[msb..lsb] := true

The structure is identical to the earlier method. In this
case, we're expecting three tokens; the second and third
must be numbers that are valid I/O pins for the
application. Remember that state is being passed as false
(0) or true (-1), and the internal constant true has all bits
set so it will work with any size group of I/O pins. We use
this to set all of the pins in the group to outputs via the

dira register. Let's do one more that is a bit more involved.

The FREQOUT command — as expected by the program
— might look like this:

FREQOUT 26 A 10

The command takes four tokens. The second token is
the pin number to use. The third token is the counter to
use; this can be "A" or "B." The last token is the frequency
in Hz. The above command would cause the LED on P26

20 NUTS2VOLTS April 2015

jeibls) jeutiat sieeve; || jos, Cieicg, lave

if (parser.token_count <> 4)
return

ie (parser toOkengers mmumbera (4)
pin) parser. eokens value (is)
ifnot ((pin => 0) and (pin =< 27))

IESE ILcIgh
else
me ture
di (((elesicie sirOltem Iein (2) == il)
Paxser ucser (parser. Loken adder (2)))
Gurwen — Oy tLollpancer. tokemmadeln (2)
ie cites <> "A™) and (cere <> "E™))}
iene Leigh
else
ree wear

ihe (Parser token ers mmumbe | (s))))

i R= jeer .colkeia welline (3))
else
rae eruerata

SSE _isiaese/ (ould, Wikies, la)

Most of this should look familiar by now. The
difference is in handling the second parameter (third
token) which is the counter module to use. The command
calls for a single letter, A or B. We start by checking the
length of the token. If it is only one character long, we
convert it to uppercase to simplify testing. Remember that
tokens are stored as strings, so we use byte[] to extract
the letter token from the string; the parser object includes
a method called parser.token_addr() which returns the
hub address where that token is stored. This allows us
direct access to it.

Okay, it's your turn. Create a new command, add it to
the token list, create the handler code, and give it a go. To
aid the development of new commands, | have a
reporting method that analyzes a new command and
provides a breakdown of each of the tokens. Figure 1
shows the report output from a few of the commands.

Easy Remote Control

As | stated earlier, the parser is generally taking input
from a serial stream; it doesn't care where that serial
stream is coming from. During development and testing, |
used PST. | have a couple personal projects that would
benefit from remote control — and this turned out to be a
breeze. For remote input, | used a Bluetooth module. At
the moment, I've tested three different units: the RN-42
module from Parallax; an XBee socket compatible RN-42
from SparkFun; and an $8 HC-06
module that is available all over the
Internet.

The control freak in me wasn't
happy to use an off-the-shelf
Bluetooth terminal on my phone, so
| knocked up a little app using the
MIT App Inventor 2. Sadly, this only
works for Android phones. Al2 uses
block-style programming which is
not really my cup of tea, so I'm
looking at other tools. Hopefully, |
can find one that lets me deploy
simple control apps on Android and
iOS products. We'll see.

The $8 HC-06 modules are very
enticing for their price, so | bought
one to try. Here's the rub: They're a
bear to configure. When in
command mode, it does not use a

terminating character (e.g., carriage return) for the
command; it uses a serial timeout. What this means is that
one cannot simply type commands in through a terminal.

| solved the problem — which also allows me to set up
the HC-06 while in the project — by creating a
configuration program that uses the parser engine.
Changing the baud rate is now simple:

BAUD 38400

Other commands allow me to set the pairing code
and the name — something | like to do with my projects.
Figure 2 is a screenshot from my phone showing that I'm
paired with the HC-06 on my Activity board (Figure 3).
I've included my RN-42 and HC-06 configuration
programs in the downloads available at the article link.

On a Personal Note

| recently received happy and distressing news on the
same topic on the same day. | learned that a friend's wife
had successful surgery to remove a cancerous tumor and
her doctors expect a full recovery — wonderful news. The
same day | learned that another friend's wife has been
diagnosed with terminal cancer — horrible news. Both of
these ladies are young and have a lot to contribute to
society.

Not many things truly upset me, but that people are
still being taken by this horrible disease does. Please
consider donating to cancer research; there are many
organizations that can do great things with your generous
donation. (Thank you for indulging my personal outburst.)

Until next time, keep spinning and winning with the
Propeller! NW

i FIGURE 3. HC-06 in PAB.

April 2015 NUTS2VOLTS 21

NEW PRODUCTS

mm HARDWARE
m SOFTWARE
m@ GADGETS

m@ TOOLS

4WD OFF-ROAD as

ROBOT
CHASSIS

ervoCity is now offering the

Nomad 4WD off-road chassis
kit which is an easy to assemble
robotic platform capable of going
places a normal chassis can’t.
What makes this chassis kit different is not only its vast
amount of attachment points for various add-ons, but also
the fact that it is easily and fully configurable.

The chassis is equipped with four 5.4" diameter by
2.25" wide heavy duty tires, four super duty/ball-bearing
planetary gearmotors with full metal gears, and a ball-
bearing pivot suspension. Also included in the 4WD
chassis kit is a large central ABS plastic body with two
large access panels that open up to a cavity large enough
for a 7.2V NiCAD/NiMH or other LiPo battery and
electronics to fit comfortably. Its central body also has a
multitude of 0.77" hub patterns and cutouts at the bottom
to run motor wires through. Since it is made out of ABS
plastic, drilling holes for additional mounting options is
simple. Retail price is $279.99.

FORCE
SERVO ARM

Iso available from ServoCity is the Force servo,

which is a new type of a servo drive for
remotely controlled devices. The majority of modern
servo drives maintain a controlled position of the
arm. Other servo drives are responsible for cyclic
rotation with variable speed. Force Servo or F-Servo
is a servo drive with controllable action force.

The value of force is proportionate to the control

signal and does not depend on the position of the

arm. A force sensor (dynamometer) is used for controlling
the force. This arm simplifies many mechanical devices
where it's necessary to control the action force created by
a servo drive or the action force of a mechanism
controlled by a servo drive. When used instead of a servo
drive with a controlled position of the arm, the arm makes
it possible to improve the technical characteristics of many
devices and mechanisms.

The key areas of application are remotely controlled
light drones, robots, radio-controlled models, and rotation
devices for video cameras. Retail price is $24.99 each.

For more information, contact:
ServoCity
Web: www-servocity.com

WIRELESS
TRANSCEIVER

emos/Radiometrix now has available the new Mini-

MURS (Multi-Use Radio Service) NiM1B-154.570-5-
12.5-MURS which is a frequency programmable narrow
band transceiver that offers a low power reliable data link
in a Lemos/Radiometrix transceiver standard pinout and
footprint. It is suitable for licensed and unlicensed VHF

22 NUTSEVOLTS April 2015

allocations and Federal
Communications
Commission (FCC) part 90
and part 95.

Features include:

* Conforms to EN 300
220-3 and EN 301 489-3
(10 mW version only).

- Standard frequency 154.570
MHz or 154.600 MHz (re-
programmable).

* Other frequencies from 120 MHz
to 175 MHz.

- Data rates up to 5 kbps for
standard module.

- Usable range over 1 km.

- Fully screened.

- Low power requirements.

* 25 kHz channel spacing.

- Feature-rich interface (true analog
and/or digital baseband).

Applications include:

- Multi-use radio service.

- Industrial telemetry and
telecommand.

- High-end security systems.
- Vehicle data up/download.
* ROV/machinery controls.

A technical summary is:

- Fully integrated sigma-delta PLL
synthesizer based design.

» High stability TCXO reference.

* Transmit power: +13 dBm (20 mW)
- Image rejection: >70 dB

» Receiver sensitivity: -120 dBm (for
12 dB SINAD)

- RSSI output with >50 dBm range
> Supply: 3.3V - 15V @ 30 mA
transmit, 18 mA receive

+ Dimensions: 33 x 23 x 11 mm
(fully screened)

For more information, contact:
Lemos International
Co., Inc.

Web: www.lemosint.com

CLAMSHELL
SPRING PIN

QFN SOCKET

Jromwece Electronics recently
introduced a new QFN socket
addressing high performance
requirements for testing QFN devices
— the CBT-QFN-7039. The contactor is
a stamped spring pin with 17 gram
actuation force per ball, and a cycle
life of 50,000 insertions. The self
inductance of the contactor is 0.75
nH, insertion loss <1 dB at 31.7 GHz.
The current capacity of each

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April 2015 NUTS#VOLTS 23

| BUILD IT YOURSELF
By Mark McGuire

In 1643, Evangelista Torricelli discovered that "we live at the bottom of a sea of air,"
and the pressure of the air could be measured with a simple column of water or
mercury. In 1648, Blaise Pascal found differences in pressure with only slight
elevation changes, leading to the idea that air has weight.

Changes in this pressure acting on evacuated bellows can be made to trace a line on
a clockwork-powered drum, indicating fluctuations in atmospheric pressure as shown
in Photo 1. You can still buy these devices which are credited to Lucien Vidi, who (in
1844) invented the practical barograph. They have been much improved, but still
require a steady platform, winding of the clockwork, refreshing of the special ink (that
must remain fluid until it hits the paper, then quickly dries), and renewing of the chart
paper. They are also expensive.

24 NUTS2VOLTS April 2015

Post comments on this article and find any associated files

and/or downloads at www.nutsvolts.com/index.php?/
magazine/article/april2015_McGuire.

idi is said to have spent years and all his money
YY: the invention of the barograph. That was a

time when the value of something was judged
to be proportional to the time and effort that went into
it. Of course, we in the modern era have been taught
to laugh at ideas like that, and think ourselves superior
because we can put together a better device with
some parts bought online and a few hours’ work.

|, for one, feel a quite satisfactory sense of
accomplishment at having duplicated — if in only a
removed sense — the device of Vidi with a graphical
LCD, a BMP085 digital pressure sensor, and an
Arduino Uno.

Photo 2 shows the breadboarded version. A
resistor, a 10K pot, the GLCD, and the Arduino — that's
it. The display lists the pressure in Pascals (named, of
course, for the aforementioned pioneer), meters of
elevation, and standard atmosphere fraction of the sea
level average. Also, there are low and high graph limits.

These limits are calculated like this: The setup
function does a reading and then it rounds this up or
down to the nearest 500 Pascals. It then adds 1,000
Pascals to the upper value, and subtracts 1,000 from
the lower one. This is so the readings will have a
chance of landing in the middle of the graph since the
device may be at any altitude when it is started.

If the pressure happens to wander to within 100
Pascals of either limit, it adjusts both limits up or down
by 500 Pascals. This creates an unavoidable
discontinuity, but the jump is obvious on the graph.
Refer to 90_hour_bmp085_GLCD_graph_baro.ino at
the article link.

There are two graphs: one for the last hour, to
show rapidly changing pressure; and one for the last 90
hours, to show the long term trend. The graphing
proceeds right to left, with the display marching as it
were to the left as new values are added to the right.
The program uses two circular buffers to store the
readings, with the newest reading overwriting the
oldest one.

See the source list for the places to download the
C code for the BMP085 and the KSO108 Graphical
LCD Library. There is a PDF file
(GLCD_Documentation.PDF) in the DOC subdirectory
of the unzipped GLCD library. This contains a correct
wiring diagram for the display; use it instead of the
HTML version which contains errors.

Due to the use of the WIRE library for the BMP085
— which uses Arduino pins A4 and A5 — the EN port of “ae i 7 mg PHOTO 3.
the GLCD needs to be changed from A4 to something ’

April 2015 NUTS8VOLTS 25

CODE SOURCES

C code for BMPO85:
https://code.google.com/p/bmp085driver/downloads/list
Graphical LCD Library:
https://code.google.com/p/glcd-arduino/

Nuits '&' Voallits
I! CD-ROMs
& lHiat; Specrall!
That's 132\issues!
Complete with supporting

code/jand media files. y
|

a3 2e| |
Onilya$22H95
or $24:95 each.
Call to order at 1-800-783-4624

or go to www.nutsvolts.com
26 NUTS2VOLTS April 2015

22 U

Temp:
Pressure:
$9381

else; | picked pin 12. This change is reflected in the
KS0108_Arduino.h file at the article link. Use this file to
replace the one in /Arduino/libraries/glcd/config (which
will be found in the Documents folder on a Windows
machine). Or, you can make this edit yourself.

Be aware that not all graphical LCDs work with the
GLCD library cited in the sources. Check the pictures of
the pins: there should be CS1 on 15 and CS2 on 16.

The version in Photo 3 uses an Arduino Nano. It is
also using a BMP180 — an updated version of the
barometric sensor. All these are functionally the same as
those mentioned previously.

ITEM

Arduino Development Board:

Uno or Nano

arduino.cc
www.sparkfun.com/products/11021
‘www.adafruit.com/products/50

KS0108 Graphical LCD

www.sparkfun.com/products/710
www.adafruit.com/search?g=ks0108&b=1

BMP085 or BMP180 Barometric Pressure Sensor

www.sparkfun.com/products/11824
Wwww.adafruit.com/products/1603

PARTS.
LIST

10K Potentiometer
www.digikey.com/product-detail/en/3362P-1-
103LF/3362P-103LF-ND/1088412

220 ohm Resistor

Wiring Graphical LCD KS@1@8 and Sensor to Arduino

BrPeSS Breakout

Rear View

Arduino

Ground

Crourd

BMPL8® Breakout

A DP-—-NUOTHOR OG Bottow
ee .
YOU OH =F
om oS eee
Ou 5

a

m@ FIGURE I.

Photo 4 shows a somewhat different program
(hour_bmp085_GLCD_graph_baro.ino) with a single
graph updated every minute. The whole thing represents
an hour.

Photo 5 shows the same Arduino-GLCD combination,
this time with a different program (general_graph.ino). This
one has the barometric code stripped out, and simply
graphs the voltage on pin A4. The same hardware setup
works here; just leave out the barometric sensor.

The entire graph spans eight hours. It is tracking the
voltage on two 18650 lithium rechargeable cells in
parallel, with a 7.5 ohm resistor load. | was curious to see
how these cells would hold up since they were salvaged
from an old laptop battery.

This illustrates how just about any slow-moving signal
(such as temperature) can be graphed with this setup.
Voltages higher than 5V can be scaled down with a
voltage divider. The time between graph samples can be
adjusted easily in the program (currently, delay (240000)
equals 240 seconds, or four minutes).

Counts per unit time from a Geiger tube could easily
be mapped into the graph range and plotted. There is a
chance that a sensor can pick up solar storms. A
Honeywell HMC5883L has a two milligauss sensitivity; a
plot of that might be interesting.

m@ PHOTO 5.

The wiring chart is in Figure 1. board type is correct and the COM port is correct. If that
doesn't work, unplug the LCD and try again (a good
A few pitfalls: Be sure to follow the instructions when reason not to solder it together).
installing the Arduino libraries. Just copy the zip file into The Arduino IDE saves programs in its folder within a
the Arduino directory, then open the integrated new folder with the program name. This can be confusing
development environment (IDE) and import the library. when you are moving things around. NV

The IDE will unzip the file; you don't have to.
If the program fails to upload, make sure the Arduino

April 2015 NUTSEVOLTS 27

omron H3t

SUPER KISS TIMER

28 NUTSEVOLTS April 2015

By Frank Muratore

Post comments on this article and
find any associated files and/or
downloads at www.nutsvolts.com

/index.php?/magazine/article/
Epril2015- Muratore.

SUPER TIMER

Have you ever built a project that needed a
load to be switched on or off at regular
intervals? Or, do you have a use for an accurate
timer to facilitate switching of lights or another
device with repetitious on/off cycles? Don't
have the money or time to buy or build such a
device? Then, the "Super Timer" is for you.

This timer not only requires a minimum parts
count, but can be built in one evening. The
timer is programmed via thumbwheel switches
and — besides having eight modes of operation
— it can run from milliseconds to 9,999 hours.
(That's over a year!) The unit is built around the
Omron H3CA-A timer module.

Caution: This project uses 120V AC line voltage in its operation.
Only persons qualified and knowledgeable in safe handling
practices should build it. If that’s not you, get help from someone
with proper experience before attempting to build it.

Other features are:

- Wide input voltage range

+ 24-240 volts AC or 12-240 volts
DC

+ Three amp output contact rating

- Isolated supply from output

+ Industrial reliability

* Compact size

+ Few external parts needed

After building the Super Timer, | got
the idea to simplify it even more while
retaining all of the features of the original.
The Super KISS (you know, for Keep It
Simple Stupid) Timer was born. This newer
module has a ton of versatility (see the

OMRON H3CA-A
TIMER MODULE

JUMPER

See Nate 1

Notes:
1. For isolated output, connect pin 11 to external
voltage only remove jumper

Connect external return to pin 2 and disconnect
from AC neutral

2. For timer with power fail protection, feed pins
10 and 2 with external battery-backed power and

sidebar).

Referring to the schematic, you can
see there are only four switches required:
two momentary normally open, and two
alternate action switches. The momentary
switches control the start and reset functions, while the
alternate action switches control the power and gate
functions. Also, you can eliminate the gate switch if you
don’t have a need to “halt” the timer operation.

Wiring is straightforward. All AC splices are soldered
and protected with heat shrink. Also, strain reliefs are used
(as dictated by the NEC). The code reads: “Connections
must be done in a manner to not pull loose while
protecting the wires from damage.” This is done (very
nicely) by the use of Arlington low profile strain reliefs
(www.aifittings.com).

To further simplify wiring, | used a store-bought line
cord and cut it in two (saving the male end for use). | took
the remaining pieces and cut off the female end, then

disconnect pin 10 to 11 jumper.
Feed load power to pin 11 and load neutral

# Timer schematic.

added my store-bought female connector (heavy duty
type).

You can buy an extension cord (of the proper size)
and use both ends (if you like) to make construction even
simpler. | prefer the heavy duty female for “knock-around”
resistance. The other ends are wired per the schematic.

Also as shown in the schematic, you can wire the
timer for power fail back-up. However, this requires a
separate source of back-up power. For simplicity, | have
opted not to do this. Also, if the power-fail option is

DESCRIPTION PART # SUPPLIER

Timer Module H3CA-A aliexpress.com

Sil, $2 275-1547 RadioShack

$3, S4 275-617 RadioShack

Socket PF113A-E Omron PARTS
Case 270-1806 RadioShack LIST
Fuse Holder 270-367 RadioShack

Fuse 2700150 RadioShack

Line Cord PC-303R Cablesonline.com

3 Prong Socket 93687 Harbor Freight

Strain Relief LPCG503 -~—s AG Electrical

Misc. Hook-up Wire 278-1222 RadioShack

@ AC cable ends.

April 2015 NUTS2VOLTS 29

Operating
Instructions

Caution: Do not change the thumbwheel
switches with power applied.

Also, do not add or remove a load with
power applied.

Operating Modes

MODE SELECTIONS

There are eight different operating
modes from which to choose. Press
the leftmost thumbwheel switch to
select the desired operation mode.
When making your choice, the
operation mode will show in the
operation mode display window. The
eight operation modes are:

A ON-delay

B Repeat (50% fixed duty cycle)
C Signal Interval/OFF-delay

D Signal OFF-delay (| )

E Interval

F Cycle One-shot

G Signal ON-delay/OFF-delay

H Signal OFF-delay ( Il )

Mode A ON-delay
(Power ON Start/Power OFF
Reset): Connect start terminals 3 and

30 NUTS2VOLTS April 2015

6. Upon application of power to the
timer, time delay period begins. At
the end of the time delay period,
output contacts the switches, either
connecting or disconnecting the
load. Output remains switched until
power is removed or a reset input is

applied.

Mode A ON-delay

(Signal Start): Power is applied
continuously. The time delay period
begins at the leading edge of the
start input. Output contact switches
when the accumulated time equals
the set time. Subsequent start signals
during or after timing will not be
accepted. The output relay will
remain switched until a reset input is
applied or power is interrupted.

Mode B Repeat Cycle — Signal
Start (50% fixed duty cycle):

Power is continuously applied. The
OFF/ON cycle is initiated at the
leading edge of the start input. The
output relay will be OFF for the set
time and ON for the set time. The
ON and OFF cycle will continue to
alternate until a reset input is applied
or power is disconnected.

Mode B Repeat Cycle — Power
ON Start/Power OFF Reset
(50% fixed duty cycle): Connect
start terminals 3 and 6. Upon

@ @ Inside wiring.

employed, the “start time”
on the power-up function
will not apply.

So, what are you
waiting for? Warm up your
soldering iron and get
busy! By the way, another
great use for the timer is
to pulse a cheap soldering
iron and make it
temperature controlled
(like the costly pro
models). Just adjust the
pulse rate time and you
will have variable
temperature. NW

application of power to the timer,
the OFF delay is initated for the set
time and then ON for the set time.
The ON and OFF cycle will continue
to alternate until a reset input is
applied or power is disconnected.

Mode C Signal Interval/OFF-delay:
Power is continously applied. Time
delay period begins on both the
leading and trailing edges of the start
input. Output contact switches
during time delay period, either
connecting or disconnecting the
load. Once the timer has timed out
from the trailing edge, it resets and is
ready for subsequent start inputs.

Mode D Signal OFF-delay (| ):
Power is continuously applied. The
output relay switches at the leading
edge of the start input, either
connecting or disconnecting the
load. Time delay period begins at the
trailing edge of the start input.
Output relay switches again when
accumulated time equals the set
time.

Mode E — Interval

Signal Start: Power is applied
continously. Timing begins at the
leading edge of the start input. The
output relay is switched, either
connecting or disconnecting the
load only during timing. The timer is

reset when power is disconnected or
a reset input is applied.

Mode F Cycle One-shot

Power-ON Short/Power-OFF

Reset: Connect start terminals 3 and
6. Upon application of power to the
timer, timing starts. The output relay
is OFF for the set time and then ON
for the set time for one cycle only.
The timer is reset when power is
removed or a reset input is applied.

Mode F Cycle One-shot

Signal Start: Power is continously
applied. The OFF/ON cycle is
initated at the leading edge of the

start input. The output relay will be
OFF for the set time and then ON
for the set time for one cycle only.
The timer is reset when power is
removed or a reset input is applied.

Mode G Signal ON-delay/OFF-
delay:

Power is continuously applied.
Timing begins on both the leading
and trailing edges of the start input.
The output relay switches when the
accumulated time from the leading
edge equals the set time, either
connecting or disconnecting the
load. It also switches for the set
amount of time from the trailing

Strain rel

Timer module.

edge of the start input.

Mode H Signal OFF-delay:

Power is continuously applied.
Timing begins at the trailing edge of
the start input. The output relay is
switched only during timing.

Note: All timer instructions and
operating modes were taken from

www.farnell.com/datasheets/17540
59.pat.

(Copyright Premier Farnell UK Limited)

April 2015 NUTSVOLTS 31

BUILD IT YOURSELF

By Bob Diaz

Post comments on this article and

find any associated files and/or
downloads at www.nutsvolts.com
/index.php?/magazine/article/
april2015_Diaz.

For years, engineers and technicians have built annoying little circuits that are easily

hidden, that beep, or chirp. The AOM (Annoy-O-Matic) brings this practical joke to a
whole new level. By using the PIC12F629, this project not only beeps, but the beep

cycle appears to be completely random — maybe once every three to eight minutes.
Despite its sophisticated operation, it's very easy for any beginning electronics

student to build. Even experienced builders will find this to be a fun little project.
32 NUTS2VOLTS April 2015

very simple. The AOM uses a minimum of parts; take

a look at the schematic and Parts List.

Like many other PIC projects I've designed, the real
power to the AOM is found in software. The AOM uses
an external RC clock, R1 and C2, for an external clock
frequency of around 32 kHz. The low frequency clock
keeps current consumption to a minimum — 168 HA to 90
UA depending on battery voltage — and allows a fresh set
of AAA alkaline batteries to last at least three months.

Microchip does not provide a lot of information as to
suggested RC values for a 32 kHz external clock (8 kHz
instruction clock), and after testing the AOM with different
voltages, | now understand why. It seems that the external
RC clock is very sensitive to changes in the supply voltage.
Refer to Table 1 for the measurements | made.

For other projects, this radical change in the clock
frequency would be unacceptable. For the AOM,
however, this change adds to the intensity of the
annoyance.

For example, when the batteries are fresh, the initial
tone is around 2 kHz every three to eight minutes. When
the batteries are near the end of their life, the tone is
around 3 kHz every two to five minutes.

| found the Datak Experimenter's protoboard with
standard IC and component spacing (#12-607) to be ideal
for building this project. If you can't find this exact board,
any small 1.8" x 1.8" standard IC protoboard will do.

Before soldering, start by drawing the parts layout on
the component side of the board; see Figure 1. As
tempting as it is to skip this step, by doing it you'll avoid
the aggravation of making a mistake and having to
unsolder and re-solder components back into the correct

E n designing the AOM, my key criteria was to keep it

m@ SCHEMATIC.

GPO GP1 GP2

av 12F629 au

CK-IN GP4 GP3
2 3.464

Seconds

place. Just be sure to double-check your work against the
schematic and Photo 1.

C1 is a tantalum capacitor; the shorter lead is
connected to the negative of the power supply. Connect
this capacitor as close as possible to the IC power supply
pins 1 and 8. This capacitor removes any noise spikes that
might reach the PIC. Also, do NOT substitute an
electrolytic capacitor. A tantalum capacitor is the best
choice because it can deal with the sudden demands for
current. The electrolytic is the worst choice because it has
the slowest response for abrupt current demands.

For all prototypes | constructed, | used a ceramic
capacitor for C2. However, | see no reason why any type
of 500 pf capacitor or other values couldn't be used. (See
"Operation & Design Notes.")

Supply Voltage vs. C1

Instruction Clock R1

R2 10KQ, 1/4W
Voltage Instruction Clock R3 1200, 1/4W
5.5V 5,395 Hz
5.0V 5,715 Hz
4.5V 6,132 Hz speaker ($1.25 each)
4.0V 6,680 Hz
3.5V 7,471 Hz program the PIC.
3.0V 8,671 Hz Eight-pin DIP IC Socket
2.5V 10,655 Hz
2.2V 12,543 Hz

@ TABLE |.

1 uF Tantalum Capacitor
(2 500 pF Capacitor, any type (see "Operation & Design Notes")
75KQ, 1/4W +5% recommended

Speaker 48Q or higher. | suggest using All Electronics CAT# SK-63, 2-1/4" 63Q

PIC12F629 DIP, plastic (PIC12F675 may be used as a replacement). You will need to

IC Protoboard, Datak #12-607 recommended

AAA, Two-cell Battery Holder or AATwo-cell Battery Holder

PARTS
LIST

April 2015 NUTS:VOLTS 33

ele 7 6 re OF
ele Eup 7? 4)

:
5
}

=
w

ee ¢ {- ele

m@ FIGURE I.

R1, R2, and R3 are 1/4W resistors; higher wattage
resistors can be used if needed. R1 sets the timing for the
RC clock. While not super critical, | suggest £5%
tolerance. R2 and R3 values are not that critical, so even if
they were off by +20%, the circuit will still work.

The best speaker | found was a small 63Q unit from
All Electronics. The small size and low cost offered the

m@ PHOTO |.

34 NUTS2VOLTS April 2015

loudest sound for the money. Larger 48Q speakers also
work, but were overkill for my wishes. Using a lower
impedance than 48Q is possible, but the volume is
reduced.

In earlier versions of the AOM, | did use 48Q mini
transducers (All Electronics CAT# PE-52), but even with
two in series, the sound was not loud enough for my taste.

Standard AAA alkaline batteries should last for at least
three months. If you wish to use standard AA alkalines,
the minimum running time would be increased to at least
six months. | chose two AAA batteries in a holder because
they were small and easy to conceal. Still, even AA
batteries aren't so large that the unit couldn't be hidden
somewhere.

The IC is the PIC12F629, but the PIC12F675 will also
work in its place. | strongly recommend using an IC
socket. Should you wish to reprogram the chip, it's easy to
remove it.

Pins 3, 4, and 5 of the IC allow for special test
features and an additional function for the AOM. Pins 3
and 5 make use of the internal weak pull-up resistors
inside the PIC. Pin 4 uses the external pull-up resistor, R2.
While you don't have to wire any connecting wire or post
to these pins, | recommend wiring at least one wire to pin
4. Once built, this pin allows for quick and easy testing.

The test/feature pins are defined as follows:

Pin 3 GP3 Fast: When connected to ground, it
shortens the timing cycle by around 1/120 of the time.
This causes the unit to beep every few seconds
(random time period); (J1).

Pin 4 GP3 10 Sec: When connected to
ground before power is applied, the AOM beeps
around every 10 seconds; (J2).

Pin 5 GP2 Pause: When connected to
ground, this pauses the time count; (NC).

Once built, you could install the batteries and
wait roughly three to eight minutes before you
might hear a beep. Both pins 3 and 4 allow you to
shorten the time you need to wait.

There are two choices for speeding up the
beep cycle: pin 3 and pin 4. Pin 4 (J2) — the 10
second cycle — provides the most information
about the circuit. Remember, this pin must be
grounded before the power is applied. Once the
power is applied, if you measure the time between
each beep, you'll have a reasonable estimate for
the instruction clock frequency, the initial beep
frequency, and the RC clock frequency.

83,000 / Seconds Between Each Beep = Instruction Clock

This should give you a reasonable estimate of the
instruction clock's frequency. With fresh batteries, it
should be close to around 8 kHz. As the batteries age, the
frequency increases.

It takes four instruction cycles to produce a single
cycle of beeps:

Instruction Clock / 4 = Beep Frequency

The RC clock is always four times greater than the
instruction clock. So, multiply the instruction clock
frequency by four to determine the RC clock frequency.
With fresh batteries, it should be close to 32 kHz.

Grounding pin 3 (J1) shortens the time delay by
roughly 1/120 of the time. This provides a quick way to
hear the random nature of the beeping without waiting
too long.

Grounding both pin 3 (J1) and pin 4 (J2) generates a
rapid string of beeps. This proved to be ideal for
measuring and testing the inductive kick in the speaker.
More on that in "Operation & Design Notes."

Pin 5 (Pause) is for possible expansion. While | have
not designed any circuit or tried anything yet, one could
attach a phototransistor or some sort of photodetector
circuit to this pin. Thus, when the lights are on, no beeps
occur; when it's dark, the beeping resumes. This might be
perfect in a bedroom where the victim only hears the
beeping when it's dark. If you chose to explore this type
of operation, you may want to shorten the time between
the random beeps.

OPERATION &
DESIGN NOTES

The one area | spent the most time testing and
exploring was the speaker. Using a 120Q resistor for R3 is
a very conservative approach to the design. This allows
you to use any impedance speaker without drawing too
much current from pins 6 and 7.

The All Electronics (CAT# SK-63) 2-1/4" speaker is
roughly 63Q resistance and around 1.5 mH of
inductance. Even under worst case conditions — an output
voltage of 3.6Q and the frequency of the tone is 1.5 kHz

—_

m@ PHOTO 2.
Testing, testing.

April 2015 NUTS8VOLIS 35

Pseudo Random
Number Generation

Most software pseudo random number generators
simulate a shift register with taps at different points. The
taps are XORed and form the input to the shift register.

The other approach is to use a look-up table to read
random numbers. Due to the limits inside the PIC's
memory, a 256 byte random number look-up table was
about the biggest | could create. This sequence would
repeat roughly every day.

In order to make the table look bigger, | have two
pointers moving through the table. The first pointer moves
forward through the table reading each number, and the
second pointer moves backwards through the table
reading each number. To generate a difference after 256
bytes, the second pointer does not move when the first
pointer is at position zero. In addition, in order to generate
a different sequence of numbers from the second pointer,
the upper and lower nibbles are swapped and some bits
are inverted on the second pointer's output.

Both pointers return two different random numbers,
where one random number is subtracted from the other.
The end result is a string of eight-bit numbers that does not
repeat until 65,536 numbers later. I'm sure a cryptographer
could find a pattern to this sequence, but the average
person will have no idea what the next number will be.

— R3 would still limit the current to under 25 mA.

Another area of concern was the inductive kick from
the speaker. Even with a three volt supply, | measured

Part Sources

818-997-1806
www.allelectronics.com

All Electronics
14928 Oxnard Street
Van Nuys, CA 91411

218-681-6674
www.digikey.com

Digi-Key
701 Brooks Avenue South
Thief River Falls, MN 56701

Jameco Electronics 650-592-8097

1355 Shoreway Road www.jameco.com
Belmont, CA 94002

Mouser Electronics, Inc. 817-804-3888
1000 North Main Street www.mouser.com

Mansfield, TX 76063

Datak Protoboard Information:
www.philmore-datak.com/protoboards.htm

www.philmore-datak.com/DatakDist.htm

36 NUTS2VOLTS April 2015

around five volts peak from some speakers. This high a
voltage above VDD might damage the chip.

The normal approach to this would be to place a
diode (like 1N914) between the positive power supply
(pin 1, VDD) and pin 6, as well as another diode between
pin 7 and pin 1. The diodes would be oriented to conduct
whenever pin 6 or 7 is a higher voltage than the positive
power supply; thus removing any spikes.

The only problem with this solution was that many of
my beginning electronics students frequently solder diodes
into circuits backwards because they don't fully
understand what they are doing. This raised the question,
"Are the protection diodes really necessary?"

In order to answer that question, both pins 3 and 4
were grounded to make the AOM output a series of rapid
beeps. The unit was tested for three weeks with supply
voltages ranging from 2.2V to 5.5V. After millions of beeps
— roughly 1,000 times more beeps than the unit will
produce in a month of normal operation — my AOM
continues to work without problems.

For those who would like to modify the design to
shorten the delay times and increase the pitch, change C2
from 500 pF to 330 pF. This would cause the pitch of the
tone to start at 3 kHz and be 5 kHz by the end of the
battery's life. The delay times would range from two
minutes to five minutes with fresh batteries, and two to
three minutes by the end of the battery's life.

Values larger than 500 pF result in a slower instruction
clock with a lower pitched tone and longer delays. Values
less than 500 pF result in a faster instruction clock with a
higher pitched tone and shorter delays. For those who
wish to try things out, try values for C2 from 1,000 pF
(0.001,F) to 200 pF.

Another area for modification is changing R2 to be a
5kQ resistor in series with a 100KQ potentiometer. An
increased resistance results in a slower instruction clock,
and lower resistance results in a faster instruction clock.
For the PIC's RC clock, R2 must be a minimum of 5KQ, to
a maximum of 100KQ.

Should you settle on a faster instruction clock,
remember that a faster clock results in increased current
consumption. If you chose to use a 330 pF capacitor for
C2 or reduced resistance for R2, you may wish to use the
larger capacity AA batteries rather than the lower capacity
AAA batteries.

Closing Comments

Over the last 1-1/2 years, I've had roughly 100
students build this project. Based on their suggestions,
several variations were tried and minor improvements to
the design were added.

One of the best suggestions was to generate a multi-
tone chirp. If you look at the source code available at the
article link, you'll see that a chirp starts at 2 kHz and then

shifts to 1.5 kHz. This shift in the
frequency makes it sound almost like
a dripping water facet.

For those who want to
experiment, not only are there
several changes to the hardware you
can make, the source code can be
adjusted as well to change the timing
or the sound. All the files, including

the .HEX file to program the PIC, can
be downloaded from the article link.

Last of all, putting the AOM
inside a box would help protect the
components and provide a better
sound from the speaker. Just make
sure there's a large enough hole for
the sound of the speaker to be heard
clearly.

Llhiic
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April 2015 NUTS2VOLTS 37

Beyond the...

Arduin

Beyond the
Arduino IDE

We’re exploring the world of
working directly with AVR
microcontrollers. In the first
installment in this series, we built
our own simplified Arduino Uno on
a breadboard. Now that we’ve
established a hardware platform to
work on, we’re going to dive into
working in a new environment.
Mask and snorkel on!

All Aboard!

The journey to working efficiently with the Atmel AVR
range of microcontrollers is an exciting one. That is, if you
enjoy learning new ways of doing things, gaining greater
control over the microcontroller, working smarter and
more efficiently, and doing things you weren’t able to
before! Convinced?

Last month, we looked at a few good reasons to start
working with the raw AVR microcontroller, and then built
our own breadboard-based Arduino Uno. We'll be using
that breadboard project this month as we get stuck into
working in a new IDE.

What's in an IDE?

An IDE — or Integrated Development Environment —
is where you spend most of your time working on
embedded projects. An IDE would normally include the
code editor, a compiler, a linker, and an uploader to Flash
the code onto the microcontroller (Figure 1). More
advanced IDEs also contain debuggers. The compiler,

38 NUTS2VOLTS April 2015

FIGURE 1: Components of a typical IDE.

assembler, and linker are called a toolchain — the most
popular for AVR microcontrollers is GCC (see [1] in
Resources).

In my software developer past, the IDE was a critical
tool in getting me working efficiently — I’d make sure |
configured the IDE so that it suited the way | liked to
work. If you've worked in other environments, you'll know
exactly what | mean.

The Arduino IDE is a great tool to get you started with
embedded systems, but it is very basic as IDEs go. The
strength of the Arduino environment lies in the way in
which some fairly complex functionality is abstracted away
from the designer in a number of libraries — you'll see as
we work through this series how functionality like reading
an analog value is made much simpler through the
Arduino IDE.

I can sense that some readers are questioning why
we’re trying to make things less simple. The answer is that
we’re trading simplicity for increased functionality and
flexibility. Stick with me and you'll see the benefits. | had a
number of false starts before | put my head down and
tackled it head on. | haven’t looked back!

Post comments on this article and find any associated files and/or downloads
at www.nutsvolts.com/index.php?/magazine/article/april2015_Retallack.

By Andrew Retallack

Good Bye Arduino IDE,
Hello ... ?

Do a quick search and you'll see that there
are a number of AVR IDEs to choose from. The
more popular ones are Atmel Studio, Eclipse with
the AVR plug-in, and IAR’s Embedded
Workbench. In fact, you could even stick with
the Arduino IDE and just ignore the Arduino
libraries. The Popular IDEs sidebar gives an
overview of some of the features of these more
popular IDEs.

Personally, | prefer to use Atmel Studio. It is
developed by Atmel (the manufacturer of the
ATmega328P on our breadboard Arduino), so |
know it'll support all my AVR microcontrollers
without any problem. Unfortunately, it is only
available for Windows, but it is dead easy to
install and use, has a good set of functionality,
and is free.

Along with the new IDE comes a host of
new ways to interact with the microcontroller —
you'll be working at a lower level without the
abstraction that the Arduino IDE provided. While
this is a little more complex, it gives you loads
more control and flexibility, and is one of the key
reasons to make the move.

What? No More
digitalWrite?

That’s right! We've left our digitalWrite(),
pinMode(), digitalRead(), and a whole bunch of
other functions behind. These functions
concealed some of the low-level instructions
needed to access the microcontroller’s
functionality — so we now need to get down and
dirty to do this ourselves. Before we roll up our
sleeves, let’s get a couple of principles out the way.

Pin Numbering

In our Uno world, we had 14 digital pins
(DO-D13) and six analog pins (AO-A5). This
numbering system was developed by the team at
Arduino to make it easier to work with the inputs
and outputs. In reality, the microcontroller 1/O pins
are divided up into “ports” and “pins.”

Pins are the physical I/O pins on the
microcontroller, excluding the various power and
ground pins. To make it simpler to access the pins,
they are grouped into ports; usually eight pins per
port. For Atmel controllers, pins are numeric (0-7)
and ports are alpha (starting at A). Each pin is

Popular IDEs

ARDUINO IDE

Many hobbyists stick with the Arduino IDE when they move onto using
stand-alone microcontrollers — just as we did in the first article. The Arduino
IDE offers a familiar environment and runs on multiple operating systems easily,
but has an extremely limited set of features. In addition it does not support a
wide range of AVR microcontrollers “out the box." | wouldn't suggest it as an
option.

ATMEL STUDIO

Atmel Studio is — as its name suggests — Atmel's own in-house IDE. It
leverages off Microsoft's Visual Studio platform, and therefore only runs on
Windows operating systems. It does, however, offer a number of benefits to the
hobbyist and enthusiast, which | believe outweigh the platform limitations. For a
start, it's free, without any restrictions on the size of code you can write. It also
uses the GCC toolchain, which is the de facto open source standard for AVR
microcontrollers. A big attraction for me was the ease of installation and built-in
support for all Atmel's microcontrollers, not just the eight-bit AVR. So, if you
move onto using Atmel's other series such as the ARM, you will work in the
same IDE. Finally, it is pretty full-featured: it uses Microsoft Intellisense to make
coding faster; has a built-in simulator to test code before it even sees a
microcontroller; and has a debugger to allow you to debug code as it's running
on your microcontroller (see [2] in Resources).

IAR EMBEDDED WORKBENCH

IAR EMbedded Workbench for AVR is a professional-level development
tool — and comes at a professional price! You do have the option to use a
code-size limited version, but as soon as your code exceeds 4 Kb in size you
need to pay up or move on. It also only runs on Windows. It is a fully-featured
IDE that allows simulation and debugging. A key advantage is that IAR has
products for many other manufacturers, so if you can manage the price it will
allow you to work in one environment for most of the microcontrollers you're
likely to use (see [3] in Resources).

ECLIPSE WITH AVR PLUG-IN

If you are a supporter of multi-platform open source software, then the
Eclipse IDE with the AVR plug-in is perfect for you. If you don't like performing
multiple downloads and complex installation processes, then this is NOT perfect
for you. Eclipse is a really great IDE and has a strong community behind it; the
AVR plug-in, however (and I'm sure I'll get shot down by someone), seems to
have stagnated since the end of 2011. If you're feeling brave, there are a
number of tutorials out on the web that should get you up and running without
too much pain (see [4] and [5] in Resources).

(PCINT14/RESET) PC6 [1] 1 } PC5 (ADC5/SCL/PCINT13)
(PCINT16/RXD) PDO (]2 | PC4 (ADC4/SDA/PCINT12)
(PCINT17/TXD) PD1 43 -] PC3 (ADC3/PCINT11)
(PCINT18/INTO) PD2 (] 4 _] PC2 (ADC2/PCINT 10}

(PCINT19/OC2B/INT1) PD3 (4) 5 -] PC1 (ADC1/PCINT9)

(PCINT20/XCK/TO) PD4 1 6 _| PCO (ADCO/PCINTS)

VCC (47 _] GND
GND (18 _) AREF
(PCINT6/XTAL1/TOSC1) PB6 C]9 _| AVCC

(PCINT7/XTAL2/TOSC2) PB7 C
(PCINT21/OCOB/T1) PDS C
(PCINT22/OCOA/AINO) PDE C
(PCINT23/AIN1) PD7 C

(PCINTO/CLKO/ICP1) PBO CL

_] PB5 (SCK/PCINTS5)

_| PB4 (MISO/PCINT4)

_] PB3 (MOSI/OC2A/PCINT3)
-] PB2 (SS/OC1B/PCINT2)

_] PB1 (OC1A/PCINT1)

FIGURE 2:
Almega328P pinout diagram from the datasheet.

April 2015 NUTS2VOLTS 39

therefore referenced by its port and pin number, prefixed
with a “P” (e.g., PB1, PBO, PD7). Figure 2 is from the
ATmega328P datasheet, and shows how the individual
pins are named — you'll notice that they don’t flow
logically from the first to the 28th pin, not all ports have
eight pins, and there’s no PORTA.

When | first looked at the pinout diagram in the
datasheet, | nearly flipped! There was so much complexity
and very little to explain what all the acronyms in
parentheses were. Don’t panic! We’ll tackle these when
we need them over the course of this series.

Registers

Okay, so we know that each of the I/O pins are
numbered differently to the Arduino IDE and how they’re
numbered. How do we read from or write to them? Most
microcontrollers use registers to do this. A register (or
more correctly, a hardware register) is a bit like a pre-
defined variable — you can read the value stored in the
register and change it (if it’s not a read-only register).

In the background, each hardware register is linked to
specific hardware-related functionality, and writing to them
causes the hardware to behave in certain ways. Registers
have specific memory addresses, but we usually refer to
them using the “friendly” names that are defined in the
datasheets and header files.

The simplest hardware registers are simply called
“PORT” registers. There is one of these registers for each
of the ports on the MCU. For the ATmega328P, there are
PORTB, PORTC, and PORTD registers. By writing to these,
you cause the individual pins to go either high or low in
the same way as digitalWrite() did in the Arduino IDE.

But which pin? A port contains up to eight pins, so
how does the PORT register allow us to access a specific
pin? Simple! Or, so | was told when | first tackled this.
However, it took me a while.

As mentioned, each port has up to eight pins. A byte
has eight bits. A register is usually one byte in size. If you
make the connection, you'll realize that each bit in the
eight-bit register is linked to a pin on that port. Figure 3
shows an example of how this would look for PORTB,
with PBO and PB4 set high.

In order to make pin PB2 go high, you need to set bit
2 of the PORTB register to a 1. To make PB4 go low, you

Pin Number PB7 PB6 PB5 PB4

Bit Number 7. 6 5

4 3 2 1 0
Pin High/Low Low | Low | Low | High
ro ct EC

FIGURE 3: Register for PORTB with PBO and PB4
set high.

40 NUTS2VOLTS April 2015

PB3 PB2 PB1 PBO

need to set bit 4 of the PORTB register to 0. Behind the
scenes, this is exactly what digitalWrite() was doing for you.
One final piece of theory before we get stuck into a
first project: bitwise operations. We need to use bitwise
operations in order to set the bits in the PORT to 1 or 0.

Bitwise Operations

Bitwise operations are used to manipulate individual
bits, or groups of bits. We won’t go into all the uses for
these operations and operators here, but will focus on
what we need them for: to set specific bits in registers.

Let’s assume you have PORTB configured as in Figure
3; bits O and 4 are set to 1 and the rest to 0. In binary, this
would be represented as 0b00010001 (where the prefix
Ob indicates a binary number follows). Now, let’s set PB2
high (i.e., bit 2 will be set to 1).

One way to do this is by spelling it out and setting
PORTB to 0b00010101. However, you can only do this if
you keep track of the values of all the other bits in the
register — i.e., you also need to know the values of the bits
that you aren’t setting. This is not very practical in a
dynamic embedded system. Bitwise operators allow us to
change the value of just PB2, without affecting (or
needing to know) the values of the other bits in the
register. Bitwise operation is critical in working with
microcontrollers.

You may have come across the bitwise operators
(AND, NOT, OR, XOR), as well as the shift operators (Left-
Shift and Right-Shift). | want to get us to a working project
as soon as possible, so | won’t delve into the detailed
theory behind these operators. What | will do is quickly
summarize what you need to know to get working.

Bitwise OR

The bitwise OR operator compares two binary values
and returns a value that includes the 1s from both of
them. In the example in Figure 4, bit 2 contains a 0 in the
original register, and a 1 in the value it is being OR’ed
with; the result is therefore a 1. Practically, if we want to
set PB2 to a 1, we simply need to perform the OR
operation: PORTB = PORTB | 0b00000100.

Bitwise AND

The bitwise AND operator compares two binary
values, and returns a value that only includes the 1s
where both of the values contain a 1. In the example in
Figure 4, we want to check whether bits 2 and 0 are set
(i.e., are 1).

By ANDing a binary value of 0600000101 (where
bits 2 and 0 are 1), we can see that only bit 0 was set in
the original register. In practice, this would look like
PORTB & 0600000101

Operator Symbol Used For

a) | (pipe) Setting specific bits to a “1”
AND & (ampersand) Checking whether specific bits
are set (called “masking”)

NOT ~ (tilde) Combine with AND to clear
a specific bit
a

Bitwise NOT

The bitwise NOT operator simply switches 1s to Os,
and Os to 1s in a binary value. It operates on a single
value, and does not do a comparison between two values
as the AND and OR operators do. The NOT operator is
useful for setting bits to a 0 when combined with a
bitwise AND.

Let’s say we want to unset PB4. First, we apply the
NOT to the bits we want to clear, and then AND the
result to PORTB:

NOL OS © OO 1 O 0 © O (Bit 4 is a 1 as this is the bit

we want to unset.)

(Result of the NOT operation.
Now, we AND it with the
value of PORTB.)

= OH OOOO OO Oi (The result is that only bit 4

has been unset.)

Bitwise XOR

Finally, we'll look at the bitwise XOR operator. This
operator compares two binary
values and returns 1 where
the corresponding bits differ,
or a O where they are the
same. This is a useful way to
toggle a bit; for example, if
you want to flash an LED on
and off. If you wanted to
toggle PB4, you would use it
like this: PORTB = PORTB *
0b00010000.

Shifting Bits

After you’ve looked at the

Description \In Code

POR!
POR!
POR!

POR!

POR!

FIGURE 4:
Summary of the
commonly used
bitwise operators.

Example

above bitwise
operation examples,
you’re probably
thinking you'll be
typing 1s and Os for
the rest of your life.
Thankfully, bit-shifting
is here to rescue you.
When | first
encountered bit-shifting, my eyes glazed over and | moved
on to something that seemed less complicated. The reality
is that it’s very simple.

Let’s say you want to refer to PB4 on PORTB (PB4 is
bit 4). You can either use the same format we used in our
example (0b00010000) or you can “left-shift” a bit into
position 5. The Left-Shift operator is a double angle-
bracket pointing to the left (<<).

A few examples explain it best:

O0b00000001 << 1 =
Ob00000001 << 4

0b00000010
0b00010000 (This is the position
of PB4)

As you know, the decimal value of a binary
0b00000001 is simply 1. So, to make your life easier, you
can left-shift the decimal value 1 to the position of PB4
which is 1 << 4.

Summarizing All the Theory

Let’s combine all the above with a few examples.
Figure 5 shows the initial values of the PORTC register,
pins 0-5, and then the changes to the pins as we perform

PC5 PC4 PC3 PC2 PC1 PCO

rC

rC

FIGURE 5: Using the bitwise operators to set register pins.

April 2015 NUTSVOLTS 41

Choosing a Programmer

There are a large number of programmers available for AVR devices — a reflection
of the popularity of AVR microcontrollers amongst hobbyists and enthusiasts. It
would be impossible to highlight them all here, so I've gone for four of the more
cost-effective ones.

Atmel AVRISP mkll In-System Programmer

This is Atmel's own programmer, so is natively supported by Atmel Studio. It, of
course, supports all the AVR ATtiny, ATmega, and ATXmega microcontrollers, so it's
a good choice if you want something that's simple to use and does what it says on
the box. It's pretty cost-effective ($34 at time of print), and is the de facto standard
for programming AVRs (see [7] in Resources).

USBTinylSP

The USBTinylSP is the programmer that | use. The attraction for me was that it was
open source (so you could even build one yourself); it's available from a number of
manufacturers in different guises (Adafruit sells them as a USBTinylSP kit, and
SparkFun as a complete board called the PocketAVR Programmer); and it comes in
at around $16. The disadvantage is that they aren't supported natively by Atmel
Studio, but we work around that fairly easily in this article (see [9] in Resources).

Atmel-ICE

This is a fairly new product from Atmel, and is, in fact, more than a programmer —
it's a debugger too. This means that you can debug code while it's running on your
AVR microcontroller — a very useful thing to be able to do as your projects
increase in complexity. It can program and debug AVR and ARM microcontrollers,
so if you're sticking with Atmel and start working on larger more powerful ARM
processors, it's a good choice. The Basic version comes in at $49, so it's not out of
reach. As soon as my local supplier gets these in stock, it's on my shopping list (see
[8] in Resources).

Arduino as an ISP

You may have come across tutorials explaining how you can use your Arduino Uno
as a programmer for raw microcontrollers. The Arduino team have written a sketch
for upload onto your Arduino Uno, that enables you to program AVR
microcontrollers. This is a great way to start, but does take your Arduino out of
circulation. Additionally, it takes a little time to connect all the correct pins. Halfway
through my first project, | ditched this and spent the $16 to buy the USBTinylSP.

the various operations shown.

Enough Theory, Please!

Programmer ATmega328

18 (MISO)
Breadboard positive power rail
i 5K

MOSI 17 (MOSI)
Breadboard negative power rail

FIGURE 6: Hooking up a programmer
to an ATmega328P microcontroller.

need to find the corresponding menu
commands for compiling and Flashing the
microcontroller. At the level we're working at,
you should be fine using this code in other
IDEs, preferably using the GCC toolchain.

Atmel Studio (see [2] in Resources) is
easy to download and install — just follow the
setup wizard.

Step 2: Connect the LED
We're going to be doing the same thing

as we did in the first article by connecting
our LED. Connect the LED and resistor in
series to PBO (that’s pin 14) on the
microcontroller.

Step 3: Connect the Programmer
In the previous article, we used an FTDI

breakout board to program the
microcontroller with our Arduino sketch. This
month, we’re going to step it up a notch and
use a “real” programmer.

There are two advantages to this. Firstly,
you don’t need a bootloader on your

microcontroller which means you can use microcontrollers
that don’t have bootloaders written for them (the previous
article discussed how bootloaders work).

Secondly, we can program any AVR microcontroller

We've buried ourselves in a whole bunch of theory,
but theory alone isn’t going to get that LED blinking. I’ve
always been the sort of person who refers to the manual
only when absolutely necessary, but when | first looked at
the cryptic code in Atmel Studio | went straight for the
theory. So, thanks for sticking out the fundamentals. |
hope it has set the scene to get that LED blinking!

Step 1: Get Prepared
The first step to get going is to download and install

your IDE. If you would prefer not to use Atmel Studio,
then you can still go along with these articles; you'll just

42 NUTS2VOLTS April 2015

with a programmer; we can only use an FTDI breakout
board for those with dedicated serial pins (more on serial
later in the series).

I'm sure you’ve seen those six pins labelled ICSP on
your Arduino Uno. They’re there to connect a
programmer. Another choice needs to be made here:
What programmer should | use? I’ve highlighted a few of
the more popular ones in the sidebar, Choose a
Programmer. For now, if you're looking for a cost-effective
one, | recommend one based on the USBTinyISP or
USBASP. If you want one later that will allow you to
interactively debug your programs, then it’s probably a

FIGURE 7: The USBTiny programmer
hooked up to the Almega328P.

good idea to buy one that supports that up-
front.

Connecting the programmer is
straightforward, with reference to the pinout
diagram in the documentation (see [6] in
Resources). Simply hook up the pins as per
Figure 6.

From looking at the above, you'll start to
see that those cryptic labels on the
ATmega328P pins actually have a meaning and
a use. Figure 7 shows what this looks like on
our breadboard.

Step 4: Write the Code
Fire up your IDE and create a new “C”

project. In Atmel Studio, click on “New Project”
and then select a “GCC C Executable Project”
(Figure 8). Choose where to save your project and
give it a name; you'll then be asked to select which
microcontroller you’re working with (Figure 9).
Based on your choice, Atmel Studio will include
the relevant header file definitions for the pins,
ports, etc.

Resources
[1] Getting started with the GCC Toolchain:
www.nongnu.org/avr-libe
[2] Atmel Studio: www.atmel.com/atmelstudio
[3] IAR Embedded Workbench:
www.iar.com/Products/IAR-Embedded-
Workbench/AVR

[4] Eclipse: www.eclipse.org
[5] AVR Plug-in for Ecplise:

http://avr-eclipse.sourceforge.net/wiki/
index.php/Plugin_Download

[6] SparkFun USBTiny Hookup Guide
https://learn.sparkfun.com/tutorials/pocket-avr-
programmer-hookup-guide

[7] Atmel Studio Supported Programmers:
http://store.atmel.com/CBC.aspx?q=c:100115

[8] Atmel Studio Supported Debuggers:
http://store.atmel.com/CBC.aspx?q=c:100112

[9] SparkFun's USBTiny-based Pocket AVR Programmer:

www.sparkfun.com/products/9825
[10] AVRDude Download:

http://download.savannah.gnu.org/
releases/avrdude
[11] Author's website: www.crash-bang.com

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FIGURE 8: Create a
new GCC C
executable project.

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tehton rage Bayore! Ardaro f 1 Bhet

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April 2015 NUTS2VOLTS 43

* Beyond Arduino 2 - 1 Blink.c
Z Listing 1: Source code for

* Nuts & Volts - Beyond Arduino #2 the project.

Blinks an LED on PBO, illustrating register
usage and bitwise operations

Author: Andrew Retallack

www.crash-bang.com

Oe ROR) Or oe aoe

/

#define F_CPU 16000000UL //Clock running at 16MHz.

//“delay.h"

Need to define this prior to including

#include <avr/io.h>
#include <util/delay.h>

//Standard support for AVR I/O registers
//Library to handle delays

int main(void)

{

DDRB = DDRB (1<<DDBO) ; //Set PBO as output - same as pinMode(x, OUTPUT)
while (1)
{
//Turn LED on
PORTB = PORTB |
_delay_ms (1000) ;

(1<<PORTBO) ; //Set PBO high - same as digitalWrite(x, HIGH)

//Delay for 1 second - same as delay (1000)

//Turn LED! off
PORTB = PORTB & (~ (1<<PORTBO) );
_delay ms (1000);

//Set PBO low - same as digitalWrite(x, LOW)
//Delay for 1 second - same as delay(1000)

o | Arduino 2 - 1 Blink - AtmetStudio ——

SEEPS OL S-iw B aiva > \ss MIB

Fae Edit View VAssistX ASF Project Build Debug Toole Window Help i
1-8) J- Taal kuBlo-o- es a) es :
i rT =

_| FIGURE 10: Choose Release
- from the menu bar.

+ ooa05.:o4

Finally, you'll be presented with a window to enter
your code into. For now, enter the code in Listing 1 into
the window (download it from the article link). We'll
dissect it once we’ve got the LED flashing.

Step 5: Compile the Code

To compile the code, first make sure that you're
working in a “Release” configuration, not a “Debug”
configuration. The Debug configuration allows you to step
through and debug your code in Atmel Studio before
you've even uploaded it to your microcontroller. We want
to compile it for the microcontroller, so choose “Release”
from the menu bar (see Figure 10). To compile, hit the
“F7” button on your keyboard. You should see a whole lot
of activity in your Output window at the bottom of the
screen; hopefully, you see a message that says:

Build succeeded.
sss======= Build: 1 succeeded or up-to-date,
0 failed, 0 skipped ======= ==

Step 6: Flash the Code
Uploading the code is pretty straightforward if you’re

44 NUTS2VOLTS April 2015

using one of Atmel Studio’s supported programmers or
debuggers (see [7] and [8] in References). Simply connect
the programmer to the USB port, click on the Debug
menu, then “Start without Debugging.”

If you’re using a USBTiny or a USBASP, then you need
to first configure Atmel Studio to use the programmer. This
is needed once-off per microcontroller and is really quick:

1. Make sure you’ve downloaded the latest version of
AVRDude (see [10] in References). AVRDude is a
command-line program that allows you to upload code to
AVR microcontrollers — more on AVRDude in a later
article.

2. Under the Tools menu, click on “External Tools ...”

3. Click “Add” and enter the following:

a. Title: Give this configuration a name

(e.g., USBTiny ATmega328P).

b. Command: This is the path to AVRDude.exe,
including the “AVRDude.exe.” On my PC, this
reads “D:\AVRDude\AVRDude.exe.”

c. Arguments: These need to be typed in
carefully. We'll go into detail at a later stage, but
for now (assuming you’re using an ATmega328P

and a USBTiny programmer) type with careful
attention to spaces:
“c usbtiny -p m328p -v -v -v -U
flash:w:$(ProjectDir)
Release\$(ItemFileName).hex:
d. Initial Directory: This is the path to AVRDude
(e.g., “D:\AVRDude\’).
e. Check “Use Output Window.”

4. Click on OK.

Figure 11 shows the settings for a USBTiny external

programmer.

|”

Once you've set up the external programmer, to
upload the code simply click on the configuration you’ve
created under the Tools menu and the program will be
uploaded. Messages will appear in your Output window,
and it should end with “avrdude.exe done. Thank you.”

Step 7: Watch It Blink
If you’ve found your way through all these steps,

disconnect your programmer’s USB cable from your PC
and connect a power source. You'll now see the steady
reassuring blink of your LED. Give a long contented sigh!

When you snap out of the LED-induced trance, move
on to the next section to see how Atmel Studio
understood the code.

Dissecting the Code

Let’s wrap up by connecting the earlier discussion on
registers and bitwise operations with the actual Atmel
Studio code. I’ve added line numbers into the listing to
make the lines easier to reference (refer to Figure 12).

Line 13: F_CPU defines the speed that the clock is
operating at in Hz. We’ve added six zeros for a value of
16 MHz, as well as a “UL” to specify that the type is an
unsigned long. F_CPU is
commonly used in
libraries; for our purposes

USSTiny ATmega328P

D:\AVRDude\awrdude. exe [=]
~¢ usbtiny -p m328p -v -v -v -U fashiw:S(Project [»]
‘DAAVRDude| tsi

| Prompt for arguments

Close on exrt

(Cox) [conc ) (pety

FIGURE 11: Configuring the USBTiny as an
external programmer within Atmel Studio.

Line 16: This is a library of utilities to perform delays.
We use the _delay_ms() function from this library later in
the code.

Line 19: Wait! Where have the setup() and loop()
structures gone? Well, there aren’t such things outside of
the Arduino IDE; just a main() function. Inside the main
function, you need to perform all your setup steps before
you enter an infinite while(1) loop. The while(1) is
equivalent to the /oop() structure in the Arduino.

Line 22: DDRx is a “direction register” for port x — it’s
similar to the pinMode() function. So, DDRB sets the
direction for each of the pins on port B. A 1 means an
output and a O means an input. The DDBO refers to pin 0.
Left-shifting (<<) a 1 by 0 positions actually leaves the 1 in
its original position — i.e., Ob00000001.

By ORing this with
the DDRB register, we are
simply setting bit 0 to a 1.

here, we need it for the
_delay_ms() function
(which resides in the
delay.h library).

Line 15: This is
included by default in new
projects, and defines
(among others) the
“friendly” names for all the
registers (ports and pins)
we use here (remember
registers are actually
memory locations). These
names are microcontroller-
specific of course.

FIGURE 12: Dissecting the source code.

In other words, we’re
telling the DDRB register
that pin PBO is an output.
Note that even though the
left shift here doesn’t
actually shift the bit to the
left (as it’s a zero), it’s
good practice to use this
syntax so as to be
unambiguous.

Line 24: This while(1)
infinite loop is the same
as the loop() function in
the Arduino IDE.

Line 27: PORTx is the

April 2015 NUTS2VOLTS 45

register containing the bits that control the high/low state
of the pins on port x — a lower-level version of
digitalWrite(). Setting bit 0 in PORTB controls the high/low
state of pin PBO; “1” drives the pin high, and “0” drives
the pin low. The PORTBO is a macro that refers to pin 0.
In the same way as we set the direction register DDRB, we
set bit O of the PORTB register to a 1 using the boolean

OR operator.

Line 28: Calls a function from the delay.h library,

all over again.

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causing the microcontroller to wait for one second. This is
equivalent to the delay() function in the Arduino IDE.

Line 31: Here, we clear bit 0 in the PORTB register,
setting pin PBO low.

Line 32: Another delay for a second, before we start

What’s Your Name?

Hopefully, the above code makes
sense. If you were to start a program
from scratch, though, how on earth
would you know the names of the
ports, pins, direction registers, and
more? The answer lies in the
confusing, often unfathomable
datasheet. They’re called datasheets
and not information sheets for a
good reason. It takes some skill and
experience to find what you need in
the 500+ pages.

For information on the I/O ports
and pins, the place to go is section
14 of the datasheet (for the
ATmega328 at least). The overview
section covers the naming of the
registers, and then goes into detail on
how to use them for general
input/output functions. | initially
found the language difficult to
understand, but eventually | started
to see patterns and worked out what
the authors were trying to get across.

The register and pin names from
the datasheet are defined in the
“io.h” file that is included by default
in all new projects. This is what
enables you to refer to them by their
datasheet names.

What’s Next?

Whew! We’ve covered a lot of
ground in this second article —
hopefully enough to get you working
on some interesting projects over the
course of the next month. We've
covered the fundamentals of creating
simple digital outputs, but I’m sure
you’re wondering how to create
programs that accept input.

Next month, we'll dig into
handling inputs from users in order to
create a more interactive project.
NV

a N EW PROD UCTS Continued from page_23.

contactor is 1.5 amps at 20°C temperature rise. Socket
temperature range is -55°C to +180°C. The socket also
features an alignment guide for precise device-to-pin
alignment. The specific configuration of the package to be
tested in the CBT-QFN-7039 is a QFN, 3x3 mm, 0.5 mm
pitch, and 10 positions with a center ground pad. The
socket is mounted using supplied hardware on the target
printed circuit board (PCB) with no soldering.

To use, place the QFN device into the socket base
and lock the double latch socket lid onto the base using
the latch. The socket uses a compression wave spring to
apply constant downward pressure, enabling the device to
be interconnected to the target PCB. This socket can be
used for hand test and quick device screening applications
with the most stringent requirements.

Pricing for the CBT-QFN-7039 is $552 each, with
reduced pricing available depending on quantity required.

For more information, contact:
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task lighting. Their super-thin flat panel design installs in
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These recessed lights have an integral heatsink for
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beam angle.

With an average current draw of 300 mA, these panel

light fixtures can provide lighting needed at a fraction of
the power cost. Various sizes to choose from include 2 x
4,2 x 2, and 1 x 2 feet.

For more information, contact:

Super Bright LEDs
Web: www.superbrightleds.com

COMPACT HIGH FREQUENCY
RECEIVER

ational RF, Inc., announces the first of several new

high frequency and shortwave receivers to be made
available in the near future. Designed specifically for the
electronic enthusiast and shortwave listener who desires a
very unique but highly functional and highly portable
shortwave radio, National RF is now offering the 75-NS-3
receiver. The receiver is available as a semi-kit in which the
main circuit board is loaded and functionally tested at the
National RF facility. The customer is responsible for
procuring the enclosure, and must do the drilling and
integration of the enclosure to the electronic assembly.

_—

The receiver is designed to cover the 3.5 MHz to 10.7
MHz frequency range, which includes the 80-meter, 60-
meter, 40-meter, and 30-meter amateur bands, as well as
several international shortwave bands, plus WWV time
and frequency standards at 5 and 10 MHz. The procured
enclosure is a potted meat can (whose copyrighted name
is synonymous with unwanted emails).

Continued on page 77

April 2015 NUTS2VOLTS 47

“Sees eeeeeevus
. oe eee Bo)
n :

3

|

By Thomas Henry

Real time clocks have all sorts of neat uses in microcontroller projects. Most
obvious would be in applications such as alarm clocks, desk calendars,
telescope controllers, smart thermostats, automatic lawn sprinklers, and so
forth. They are also useful for creating timestamps in recordings, logged data
from weather stations, hourly energy usage reports, and much more.

hile it’s certainly possible to roll your own
microcontroller clock with the addition of
little more than a clock crystal and some
assembly language, in this golden age of
inexpensive electronics for DIY, it makes more sense to go
with a dedicated add-on device. This article introduces
you to the world of timekeeping with just such a module:
the popular and inexpensive TinyRTC.

The TinyRTC unit is a complete clock/calendar set to
shoulder all of the timekeeping duties within your circuits.

48 NUTS2VOLTS April 2015

It’s readily available from a wide range of suppliers for
around six bucks.
You’re going to love the TinyRTC’s features:

* Clock/calendar

- 4096 bytes of EEPROM

- 56 bytes of user RAM

- Rechargeable backup battery

* Communicates effortlessly along the ’'C bus

- Dedicated pulse output for interrupt applications

Post comments on this article and find any associated files and/or downloads at www.nutsvolts.com/

index.php?/magazine/article/april2015_Henry.

FIGURE I.

When you get right down to it, the TinyRTC is really
little more than a breakout board for the DS1307 clock
chip and the AT24C32 EEPROM. So, everything described
in this article can be applied to those two ICs should you
really want to tax your eyes and solder up some surface-
mount chips on your own. You can spot the two tiny
integrated circuits in Figure 1.

The reverse side (shown in Figure 2) shows the
rechargeable lithium-ion battery in its piggyback holder. If
it isn’t obvious, this means that the clock continues to
keep time even if main power to the circuit is absent.
When power is there, the battery is kept fully charged.

It’s pretty clear that the module was originally created
with the Arduino crowd in mind. In fact, that community
already has libraries available for
putting the TinyRTC through its paces.
Many people — me included — prefer
working from scratch with the PIC for
customized minimalist
implementations costing far less than

the Arduino approach, however. Does P*wisteF #

FIGURE 2.

particularly handy when printing things out to an LCD,
among other things. Recall that in this scheme, a single
byte (eight bits) can store a two digit number; the lower
nibble specifies the unit’s place, and the higher nibble
gives the ten’s place. As it turns out, when referring to
time and date, not all of the bits within the higher nibble
will be needed.

For example, with minutes and seconds, the greatest
number which can occur is 59, meaning that only three
bits are required to represent the ten’s place digit.

What about dates? The largest number you’ll have to
worry about is 31 — the greatest number of days to
appear in a month. In this case, only two bits need to be
spent in the higher nibble to represent that ten’s place

6 5 4 3 2 1 0

Minutes: Units

7
wows [ot [omnes | emt

=—_

Hours: Units

Ill show you how to easily get the
TinyRTC up and running on a PIC and
— best of all — in the easy-to-use Basic
language. Let’s tuck in.

Register 2

that mean we have to start all over
again in assembly language? Not at all! fo | 0 | Hows: tens
0O-am Hours: ;
[espe] om
rete [ope ]* | oma
rete [omme [mm |
Month:
Tens
ee

Register 3
All About the : :
oe egister
Clock Registers
As mentioned, at the heart of the Register 5
TinyRTC is the well-known DS1307
chip. Within this IC are eight registers Register 6
which allow you to set things up and
monitor the time and date. Figure 3
gives the details. Though pretty self- Register 7

explanatory and complete, there are a
few points deserving a little extra
explanation for newcomers.

The various numbers stored within
these registers are in binary-code-
decimal (BCD) format, which is

is low, the output simply follows the value of
Out (bit 7).

Date: Units

Year: Units

RS1 RSO OUTPUT

When SQWE is high, RSO and RS1 contro!
the Square Wave output, according to the 1 Hz
scheme at the right. Otherwise, when SQWE

4096 Hz

8192 Hz
32768 Hz

FIGURE 3.
April 2015 NUTS2VOLTS 49

digit. The TinyRTC takes advantage of any bits not needed
for other purposes, or sometimes just locks them to zero.
For example, bit 7 of Register 0 is used to turn the clock
on or off. If high, then the clock is halted, but if cleared it
takes off running.

Register 2 can be used in two different ways as shown
in the figure. If its bit 6 is low, then time is represented in
24 hour mode (so-called military time). On the other
hand, if bit 6 is set, then time is stored in a 12 hour
format. In the latter case, bit 5 tells you if the hour is
before or after noon; it’s cleared for the former, or set for
the latter.

The other time and date registers should be pretty
obvious, so let’s turn to Register 7 which controls the
output pin labeled SQW, standing for “square wave.” This
pin is brought out on the TinyRTC and can be used in a
couple interesting ways. As the figure indicates, if bit 4 is
set, then a square wave is generated on the SQW pin. The
bits labeled RSO and RS1 let you set the frequency at 1
Hz, 4.096 kHz, 8.192 kHz, or 32.768 kHz.

The 1 Hz option is particularly attractive since it could
be employed to generate microcontroller interrupts once a
second; say, to take a new temperature reading, or just to
flash the colon between the hours and minutes of a
display. If bit 4 is cleared, then the output pin simply
follows the state of bit 7 which gives you software control
of SQW. Take a moment to look over the figure one last
time. While it might appear mysterious at first blush, you'll
find yourself at home with it quite soon.

Bring On the Memory

As mentioned earlier, the TinyRTC gives you access to
56 bytes of general-purpose RAM within the DS1307
chip; you can use this any way you want. The addresses

Purpose
Turn clock on or off
Reset clock to manufacturer's default
Set date, day of the week, time, and hour mode
Set only the time
Set only the date and day of the week
Read date, time, and am/pm flag
Read only the time and am/pm flag
Read only the date and day of the week
h
e

I

Choose 12 or 24 hour clock mode

Set SQW output frequency

Write to clock register or RAM

Read from clock register or RAM

Write a byte to the EEPROM

Read a byte from the EEPROM

Write a string or array to the EEPROM

ead a string or array from the EEPROM
Figure 4.

e()

RTC_Read()

eepByteR()
eepArrW()
eepArrR()

Command

RTC Read)
jeepByteR()
jeepArrW)
leepArrR)

Ps)

50 NUTS2VOLTS April 2015

follow immediately after the registers described previously.
So, RAM lives at locations 8 through 63.

We normally think of RAM as temporary memory.
Thanks to the backup battery, however, it now becomes
nonvolatile — at least as long as you keep the cell in place.

The AT24C32 IC provides 4096 bytes of genuine
nonvolatile EEPROM storage. This might prove useful for
such things as storing messages to be displayed on an
LCD at times directed by the clock (birthdays,
appointments, warnings, etc.) or perhaps for logging data
from outboard sensors (light, temperature, humidity, and
so forth). In any event, the RAM and EEPROM are there
for the taking, so feel free to drink deeply of them.

Start Commanding
the Module

Both the DS1307 and AT24C32 chips on the TinyRTC
module are ’C devices. If you’ve played with this
synchronous communication scheme before, then you'll
know that the two lines called SCL and SDA (clock and
data, respectively) must have pull-up resistors on them.
The TinyRTC includes these. Even though both chips are
hanging on the SCL and SDA lines, only one set of pull-
ups is required.

| hope | haven’t frightened you with the mention of
’C — a scheme that seems daunting at first. For, in fact,
the software library put together especially for this article
takes all of the wailing and gnashing of teeth out of it! A
handful of higher level commands is all you need to start
doing something useful at once. Let’s see what they look
like. The software to drive the TinyRTC has been written in
Great Cow Basic. This is an amazingly full-featured,
powerful, yet easy-to-use compiler. Best of all, it’s open
source and absolutely free of charge. You can download it
from _gcbasic.sourceforge.net. You can fetch this article’s
source code from the article link.

Apart from the four demonstration programs that we'll
get to in just a moment, there are two other files of note.
These are general-purpose include files which add ?C and
TinyRTC commands to the Great Cow Basic compiler.
They’re titled “I2C-Alt.h” and “TinyRTC.h,” respectively.
(Be sure to view the “ReadMeFirst.txt” file for any
updates). Actually, the ?C stuff will be invisible to you, and
is required only by the TinyRTC file. Of course, you’re
certainly welcome to dip into whatever’s there should you
wish to modify the TinyRTC commands or create new
ones which occur to you. That’s the beauty of open
source software.

So, what are these high level commands? Figure 4
lists them. These should all make a great deal of sense.
There are commands to set the time, read the date, set
the SQW output frequency, read and write to the
EEPROM, and so forth. To cut down on confusion in the
figure, the parameters aren’t shown. Instead, if you head

to the include source file “TinyRTC.h,”
you will find a very thorough
description of what each command
does and what parameters are required.
The code itself is completely
commented from top to bottom should

4 : ic2

you wish to learn how it all works. TinyATC

Incidentally, Great Cow Basic has a Module
very rich set of string commands, and
it’s a snap to read or write not only
bytes to EEPROM, but also entire strings
or arrays. Slick! +5V

2 ] ona908

Time for Some a)
Experiments &: nd

Enough of this palaver. Let’s head ae =
straight to the lab and start doing 4300
something on the breadboard. I've put
together four experiments you can try oy DI
right away. Figure 5 shows the LED
schematic for everything. The source +5V
files for each experiment are also at the = 9
article link. As usual, the code is heavily para
documented, so take time to read over At
the comments to learn even more 10K
about how this remarkable module can
be harnessed.

Back to the schematic. Apart from
the TinyRTC, there’s absolutely nothing =
exotic appearing here. In fact, you
probably have all of the required parts Sunes

in your lab right now; everything is
completely generic. The entire affair can
be breadboarded in under 15 minutes,
yet reveals just about every aspect of
the TinyRTC. Before starting, do take
the usual precaution of double-checking the power
connections (+5V and ground) to both the clock module,
as well as the PIC.

Incidentally, | used the common and inexpensive
PIC16F88, but Great Cow Basic makes it a snap to change
over to some other PIC if you prefer. The ?C routines at
the heart of this are software in nature (“bit-banging”) and
so will work on most any pin of most any PIC.

In Experiment #1, you'll learn how to read from and
write to the RAM one byte at a time. The LCD actually
displays the instructions, so go ahead; run it and see for
yourself. Experiment #2 is similar, but now communicates
with the EEPROM; again, one byte at a time. In
Experiment #3, you'll write an entire string to EEPROM in
one fell swoop.

Finally, Experiment #4 is the one you've been waiting
for: a complete clock project. You can set the date and
time, and it takes off in perpetuity, with the LED blinking

+5V
A3, A4 MODE
9 + 10k $2
18 peal
©
17 a taal
©
SET
16
15 a
5 Ic1 14 =
PICT6F88 =
C1
— & 8 O.1pF
: al.
8
+5V

LCD1
2 X 16 HD44780 Compatible LCD Display

A 0.1 pF decoupling capacitor should also be used on LCD! (not shown).
Choose R2 to match the backlight requirements of the LCD used.

once per second. Even if you disassemble the breadboard
and set the TinyRTC back up on the shelf, it still keeps
time thanks to the lithium-ion battery.

One last thing before turning you loose to design your
own custom applications. It’s only natural to wonder
about the accuracy in a time-keeping device. The DS1307
within the TinyRTC is reasonably well-suited to many
common applications. | find mine loses about three
seconds a day. Naturally, this changes according to
temperature and who knows what else — even under
crystal control. If this concerns you overly, then you'll be
interested to know there is a TinyRTC clone featuring the
DS3231, which contains an integrated temperature
compensated crystal. (The EEPROM remains the same).
While considerably more accurate, it’s still backwards
compatible with the TinyRTC include files and programs of
this article.

So, get tick-tocking on your PIC today... NV

April 2015 NUTS2VOLTS 51

By Craig A. Lindley

Driving
LEDs
with a
Microcontroller

One of the first experiments people learning about microcontrollers usually
perform is how to control an LED. Typically, they hook up an LED in series
with a current-limiting resistor, connect it to an output pin, and write some
simple software to make it blink. The Arduino blink sketch shown below is
an example:

Post comments on this
article and find any
associated files and/or
downloads at
www.nutsvolts.com/
index.php ?/magazine/article
apri Lindley.

int led = 13;

// the setup routine runs once before the loop() function
void setup() {
// initialize the digital pin as an output.

pinMode(led, OUTPUT) ;

// the loop routine runs over and over again forever:
void loop() {
digitalWrite(led, HIGH) ; // turn the LED on (HIGH is the voltage level)
delay (1000) ; // wait for a second
digitalWrite(led, LOW) ; // turn the LED off by making the voltage LOW

delay (1000) ; // wait for a second

oO Arduinos, there is an LED and current-limiting
DBresistor on board already (and connected to pin
13), so there is nothing really to hook up for this first
experiment. Once this sketch is downloaded onto your
Arduino, you should see the onboard LED blink on and off
until power is removed.

52 NUTS2VOLTS April 2015

As you might expect, the thrill of watching the LED
blink wears off pretty quickly. Next, people might want to
try and control the brightness of an LED with software.

The following Arduino fade sketch causes the LED
connected to pin 9 through, say, a 470 ohm resistor to
ground, to go from off to full brightness and then back
down, over and over:

int led = 9;

is attached to
int brightness
int fadeAmount
fade the LED by

// the pin that the LED

0; // how bright the LED is
5; // how many points to

// the setup routine runs once before the loop ()
function
void setup () {
// declare pin 9 to be an output:
pinMode (led, OUTPUT);
}

// the loop routine runs over and over again
forever:
void loop () {
// set the brightness of pin 9:
analogWrite(led, brightness) ;

// change the brightness for next time through
the loop:
brightness = brightness + fadeAmount;

// veverse th
ends of the fade:
if (brightness == || brightness == 255) {
fadeAmount = -fadeAmount ;

direction of the fading at the

}

// wait for 30 milliseconds to see the dimming
effect

delay (30);
}

In this sketch, an analogWrite statement is used to
control LED brightness instead of the digital/Write
command used to turn the LED off and on as in the
previous sketch. Brightness control works using a
combination of persistence of vision coupled with Pulse
Width Modulation, or PWM for short.

Persistence of vision is an effect where our eyes and
brain hold onto an image we see for approximately 1/25th
of a second before it fades away. We all experience this
effect at the movies where we fail to notice that a motion
picture screen is actually dark about half the time. Motion
pictures project one new frame every 1/24th of a second.
Each frame is shown three times during this period. Our
eyes retain the image of each frame long enough to give
us the illusion of smooth motion. How does this relate to
LED brightness? Glad you asked.

An LED — being a semiconductor device — can be
switched on and off very quickly. An LED is at full
brightness when it is on all of the time over a fixed period
of time. If the LED is only on half of the same time period
(and off the other half of the time period) and the time
period is very short, it will appear approximately half as
bright. Now, if this switching happens at a fast enough
rate, our persistence of vision will not perceive the LED as
being turned on and off or flickering, but will perceive it
as being on at some brightness level.

PWM divides up the periodic time period into
intervals based on the resolution of the hardware. On
most eight-bit microcontrollers, eight-bit PWM is
supported. This means that there are 256 unique durations

from always off to always on. Duty cycle is defined as the
ratio of on to off times. A PWM output that is on half of
the time has a 50% duty cycle.

Figure 1 illustrates various duty cycles of a PWM
output. The green lines in this figure show the periodic
nature of the PWM output. If a PWM output is used to
control LED brightness, the frequency of the PWM output
becomes important. Flickering of the LED will be visible if
the PWM frequency is too low. Most — if not all —
microcontrollers allow the frequency of their PWM
outputs to be configured.

The analogWrite function in the previous sketch sets
how long the PWM output connected to the LED is on;
analogWrite(0) means the output is never on and the LED
is dark; analogWrite(255) means the PWM output is
always on, so the LED is at full brightness. Values between
0 and 255 determine the relative brightness of the
connected LED.

We should quickly say a few words about current
limiting with LEDs. Current limiting is important to protect
both the digital output of the controller driving the LED
and the LED itself from burning out. To figure out the
value of a current-limiting resistor to use with an LED
requires three pieces of information. First, the supply
voltage used to drive the LED (Vs); second, the current (I)
you want to operate your LED at; and third, the forward
voltage (Vf) drop of the LED. Forward voltage varies by
the color of the LED. A red LED typically drops 1.8 volts
whereas a blue LED may drop 3.3 volts.

As an example, assume our supply voltage is five

Pulse Width Modulation

0% Duty Cycle - analogWrite(0)

25% Duty Cycle - analogWrite(64)
50% Duty Cycle - analogWrite(127)

Sv
Ov

75% Duty Cycle - analogWrite(191)

100% Duty Cycle - analogWrite(255)

FIGURE |. Pulse width modulation and duty cycles.
April 2015 NUTS2VOLTS 53

€
€
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cC
¢
C
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@e0230220e0e0e0@
e0e220220e0000@

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ie@e@e0e0e@e@e@8@

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hoe if
“*ese***

FIGURE 2.The demonstration hardware.

volts; assume we want 20 mA (0.02 amps) of current for
the LED, and the voltage drop across the LED is 1.8 volts.
Using Ohm's Law, we can calculate the required resistance
with the formula:

R= (Vs - V£) / I

which works out to be around 160 ohms. If the resistor
value you calculate turns out not to be a standard value,
pick the next larger value to be safe.

Okay, so now we see how the brightness of an LED

Oty Part Description Source
1 Display 1 Common anode 8x8 RGB LED matrix eBay
1 U2 24-channel PWM controller Adafruit
1 U1 Teensy 3.1 controller pjrc.com
8 R1-R8 4.7K 1/4 watt resistor Radio Shack
8 01-08 P channel power MOSFETs SparkFun
1 Breadboard RadioShack
1 USB cable with five-pin micro-B plug

for connecting Teensy to a computer

or USB power supply pjrc.com
1 Optional USB power supply

capable of at least 1A @ 5V RadioShack

54 NUTS2VOLTS April 2015

can be controlled using PWM. With this information, you
could control the brightness of a red, green, blue, or any
single color LED with software. What if you want variable
color output from an LED? In this case, you would
probably choose an RGB LED for this purpose. RGB LEDs
actually contain red, green, and blue LEDs internally. This
means three PWM channels would need to be used to
control the brightness and the color of a single RGB LED.
By varying the duty cycle of each of the LEDs inside the
RGB LED, many color combinations are possible. If eight-
bit PWM is used on all three channels driving an RGB
LED, there are theoretically 256 x 256 x 256, or over 16
million possible color combinations. Research has shown
the human eye can discern approximately seven million
unique colors.

On most Arduino boards (those with the ATmega168
or ATmega328), PWM is available on pins 3, 5, 6, 9, 10,
and 11. On the Arduino Mega, it works on pins 2-13 and
44-46. Older Arduino boards with an ATmega8 only
support PWM on pins 9, 10, and 11. On the Teensy 3.1
microcontroller that | typically use, PWM is available on
pins 3, 4, 5, 6, 9, 10, 20, 21, 22, 23, 25, and 32.

So, as you Can see, on typical microcontrollers there
are only a small number of PWM outputs available for
driving LEDs. If you only want to drive single color LEDs,
you may be okay, but if you want to drive a large number
of RGB LEDs the outlook is bleak.

There are many options available for driving larger
numbers of LEDs using hardware external to but
controlled by a microcontroller. If you search the Internet,
you will see many examples. Many designs use 74HC595
shift register chips to drive the LEDs, but my current
solution of choice is the Adafruit 24-channel 12-bit PWM
LED driver with SPI interface (product #1429; available for
$14.95). With its 24 channels, you can control 24 single
color LEDs or eight RGB LEDs with the added advantage
of 12-bit PWM, giving finer grain control than the eight-bit
PWM described previously.

An additional advantage is that each PWM output
provides constant current, so current-limiting resistors are
unnecessary. In fact, one resistor on this driver board
controls the current through all channels which is set at
the factory to 15 mA. Up to 30 mA of drive current per

channel is possible by changing the resistor.
NOTE: This device is a current sink. It sinks
current to ground; it cannot source current.

The Adafruit device is really just a breakout
board for the TLC5947 controller chip from TI.
This breakout board makes all of the TLC5947
signals available in an easy-to-use configuration
without having to deal with surface-mount
components.

The TLC5947 chip is a cascadable shift
register with built-in PWM counters and PWM

oscillator. Since each output requires 12 bits of
information to control its PWM hardware, a total of 288
bits or 36 bytes of data must be streamed into the chip via
SPI to control its 24 PWM outputs. (More on how to
control the TLC5947 chip in the software section).

For many of my projects, a single Adafruit driver
board still doesn't have enough outputs to drive large
numbers of RGB LEDs. | recently purchased some 8x8
RGB LED matrices for use in a project. Think about it. This
is a matrix of 64 RGB LEDs which equates to 64 x 3, or
192 individual LEDs needing PWM control.

There were two ways to go about this project.
Purchase and connect eight of these boards together
somehow so each board controls one row of the display
for a total driver cost of $119.60. Or, use one of these
boards, eight cheap P channel power MOSFETs and some
clever software to control the entire display.

Being frugal, | chose the latter. In the discussion to
follow, | will show you how to use multiplexing of the LED
driver to accomplish this feat.

Multiplexing

Multiplexing is a term from the telecom industry
which meant to combine multiple channels of data onto a
single medium for transmission. Multiplexing reduces the
cost of hardware, and because of a reduced parts count
increases reliability.

Multiplexing many channels of data onto a single
medium required that each channel of data be given its
own time slot. This is referred to as TDM, or Time Domain
Multiplexing. We can use this same technique for

controlling our LED matrix by assigning each row of the
display a different time slot for update. If we update each
row of RGB LEDs fast enough, persistence of vision will
make it appear that each LED is individually controlled.

| designed some hardware to demonstrate control of
an 8x8 RGB LED matrix using multiplexing. The hardware
is shown in Figure 2 and the hardware's schematic is
shown in Figure 3.

The Demonstration
Hardware

The 8x8 RGB LED matrix | will control is of the
common anode variety. What this means is that each row
of the display has the anodes of each red, green, and blue
LED connected together (see Figure 4). The cathodes of
each column of the same color LEDs are also connected
together and brought out to pins on the matrix. By
applying a current source to a specific row pin and a
current sink to a specific cathode pin, a single color LED
can be illuminated.

| tested the LED matrix I built into the demonstration
hardware using a nine volt battery and a 1K ohm resistor
by connecting the + side of the battery through the
resistor to a row pin, and connecting the - side of the
battery to the various column pins. As you move the
battery connection from one column pin to another, you
will see the LEDs change color.

As mentioned, in the demonstration hardware, P
channel MOSFETs are used as the current source for each
row of the matrix. The current flowing from the drain of
the device into the row of LEDs is controlled by the

av ar @ 08 on 05 a6 ar 08
PCHAM MOSFET P COUN MOSFET P CHAN MOSFET P OMAN MOSFET PHAN MOSPET P CHAM MOSFET P CHIN MOSFET P CHAN MOSFET
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ROW) SEL ROW SEL ROWE SEL PWS SEL ROWS SEL AOWS SEL a ROWE SEL now? seu ®

tp se pont g te +E )
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CANT URW

NOTES
1. Demo harthwave powered by USB
2. Allvegistors 4.7K 14 wat
3. MOSFETS are SparkFun Part Number: COM-10340

COLIB ROW!
COLZB ROWe
COLIB ROW
COLuB ROW

BX8LEDMATRIX

FIGURE 3. Demonstration hardware schematic.
April 2015 WNUTS2VOLTS 55

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aa
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pr RED te BLUE

FIGURE 4. Common anode RGB LED matrix
schematic.

voltage applied to the gate of the MOSFET. As wired,
current flows to the LEDs in the row if the gate is driven
low by the Teensy 3.1 controller. If the gate is pulled up to
the voltage at the MOSFET's source pin, current flow
stops. Each row MOSFET is connected to a different pin
on the Teensy so that each can be individually controlled.

The current sink side of the equation is handled by
the TLC5947 chip on the Adafruit board. The 24 PWM
channels provided by the chip are connected to the 24
color column pins of the LED matrix. The data used to
control the PWM outputs is streamed serially into the
TLC5947 chip via the SPI interface on the Teensy
controller. A data and a clock line are used to move the
data which flows in one direction only.

Two other signals are needed for control of the
TLC5947 chip. The first is labeled /OE on the Adafruit
board, but called BLANK on the chip itself. When BLANK
is high, all of the PWM channels stop sinking current and
the chip's internal PWM counters are reset to zero. When
BLANK goes back low, the current sinks are enabled and
the PWM counters start counting.

The second control signal is labeled LAT on the
Adafruit board but called XLAT on the chip. The rising
edge of this signal causes the data contained in the
TCL5947's shift register (loaded via SPI) to be transferred
to the individual PWM counters backing each output pin.

| used a Teensy 3.1 controller from pjrc.com for
controlling the hardware. It has plenty of RAM and Flash
memory for coding up any kind of display patterns you
can envision. The Teensy is Arduino compatible via the

56 NUTS2VOLTS April 2015

Teensyduino software available at the website.

The hardware works as follows (under control of the
software which will be described next): Data for a row of
LEDs is moved from the controller to the TLC5947 chip
using SPI. The data is latched into the chip on the rising
edge of XLAT, and then the appropriate row select output
is brought low to enable the LEDs in the row. Next, the
BLANK line is driven low which causes the PWM counters
to start and the LEDs in the selected row to illuminate.
After a precise period of time, data for the next row is
loaded and the whole process repeats indefinitely.

The Demonstration
Software

The software running on the Teensy 3.1 controller is
what makes multiplexing of the LED matrix possible.
Multiplexing makes the hardware simpler, but the software
more complex. The demonstration software sketch is
available at the article link if you would like to duplicate
what | have done or use pieces of the software in projects
of your own. The sketch requires the TimerOne and the
spi4teensy3 libraries to be available in your Arduino build
environment. Please refer to the LEDMatrix8x8.ino sketch
for the discussion that follows.

The first order of business in the sketch is to define
the control signals/pins of the Teensy controller which will
control the TLC5947 chip. The assignments are as follows:

// PWM driver control pins

define LATCH PIN 9
define BLANK PIN 10
// LED Matrix row select pins
#define ROWO PIN 16
#define ROW1 PIN 17
#define ROW2 PIN 18
define ROW3 PIN 19
define ROW4 PIN 20
define ROW5 PIN 21
#define ROW6 PIN 22
#define ROW7 PIN 23

An interrupt on the Teensy 3.1 controller is used to
generate the precise timing required to make multiplexing
work. The three values below define interrupt timing:

// Interrupt period calculations
#define DATA _XFER_TIME USEC 13
#define ROW DISPLAY TIME USEC 1024

#define INTERRUPT TIME USEC

7 MS (DATA_XFER_TIME
+ ROW DISPLAY TIME USEC)

_USEC

DATA_XFER_TIME_USEC is the time in microseconds it
takes for the spi4teensy3 library to transfer 36 bytes of
row data from the Teensy running at 96 MHz to the
TLC5947. The ROW_DISPLAY_TIME_USEC is a little more

difficult to describe. It is the time it takes the TLC5947
PWM counters to count from zero to 4095, thereby
completing the 12-bit PWM cycle. The PWM oscillator
internal to the TLC5947 runs at 4 MHz under normal
operating conditions. The period of the 4 MHz oscillator
times 4,096 equals 1,024 microseconds.

Since both of these processes must occur for every
row of the LED matrix data, the total time between
interrupts is their sum. The TimerOne library is used to
cause a periodic interrupt at this frequency.

Finally, we define the frame buffer which contains the
data used to drive the complete LED matrix:

// Frame buffer definition

#define NUMBER OF ROWS 8
#define BYTES PER ROW 36

// Frame buffer is 2D array of bytes
byte frameBuffer[NUMBER_OF ROWS] [BYTES PER ROW];

Foreground code in a sketch would put data into the
frame buffer that represents the pattern to be displayed,
and the background code contained in the interrupt
service routine (ISR) moves the data from the frame buffer
to the hardware continuously. The LED matrix is updated

around 122 times per second by the ISR.

From the foreground's code perspective, it just sets
pixels to specific colors and these colors magically appear
on the LED matrix. It is not necessary to call any kind of
show function to force a display update; it all happens
automatically and in real time.

With this understanding, most of the code in the
sketch should now be self-explanatory. As a demo, |
coded a scrolling "Nuts and Volts" text message and a
swirling rainbow pattern which alternate. If you build the
demonstration hardware and run this sketch, you will see
a bright vibrant display without any flicker whatsoever.

The demonstration hardware can control 64 RGB
LEDs or 192 single color LEDs. If this is still insufficient, it
should be possible to add up to eight additional rows of
LEDs. It is also possible to chain TLC5947 chips. Sixteen
rows of LEDs combined with two TLC chips would bring
the total RGB LED count to 256 with a refresh rate of
approximately 60 frames per second. Not too shabby for
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April 2015 WNUTS2VOLTS 57

“THE DESIGN CYCLE

I

lm™@ BY FRED EADY

The RN4020 PICtail Plus BLE

Bluetooth has morphed yet again, and it seems that everybody wants Bluetooth on their

iPhone or Android phone. These days, Bluetooth Low Energy (BLE or BTLE) is the new "must

have" control and monitoring medium. The new crop of BLE radios are (as a whole) easy to

use. Most every manufacturer's BLE radio entry has an associated firmware API (Application

Interface). Many of the new BLE platforms employ simpler data interfaces which are based

on good old RS-232. The iPhone and Android application creation barriers that have for too

long impeded interactive BLE control are falling like hot rocks from a caveman's hands. In

this edition of the Design Cycle, we will take a look at the latest BLE offering from Microchip.

RN4020

The Microchip RN4020 is a qualified and certified
Bluetooth 4.1 radio module. The RN4020 takes its
instructions via ASCII commands over a UART
connection. Everything the RN4020 needs to transmit and
receive is packed in under the module’s shield. There are
also under-the-hood provisions for analog and digital |/O.
In that the RN4020 can operate alone under control of its
internal scripting engine, a resource-rich microcontroller is

RN4020-PICTAIL
Ome ochip

sip F
wi Technology In

2ee0lee8 eee ee eo@
igd@eeeeeeoe ee &€ @ @

@ Photo 1. The RN4020 PICtail is designed to allow us to
come up to speed quickly on the RN4020 hardware and
API. Almost everything we need to evaluate the RN4020
is soldered onto the PICtail printed circuit board.

58 NUTS2VOLTS April 2015

not required to assist the RN4020. A pair of connected
RN4020s is perfectly capable of taking care of themselves
with little or no help from outsiders.

Bringing Up Baby

You are reading this column, which means you are
also perfectly capable of reading the RN4020 datasheet.
So, instead of spouting RN4020 technical specifications
and I/O capabilities, let’s discuss the RN4020 in the
languages of ASCII and C. Our RN4020 hardware will be
represented by the Microchip RN4020 PICtail which you
can see under the lights in Photo 1.

BLE radios split up as centrals and peripherals. The
peripheral radio advertises its connection status, while the
central radio starts the connection process. When a pair of
BLE radios connect, the next thing they do is bond. Once
the radios have bonded, security items are saved and used
for the next connection between the two devices. Bonded
radios cannot cheat and connect to other devices.

Controlling the RN4020

Figure 1 is a skeletal pinout of the RN4020 BLE radio
module. The WAKE_SW, CMD/MLDP, and WAKE_HW pins
are responsible for initiating RN4020 state changes. The
status of the RN4020 is reported by three output pins
(PIO1, PIO2, PIO3). Let’s check out the various RN4020
states and their consequences beginning with the
WAKE_SW pin.

The WAKE_SW pin (pin 7) controls the RN4020
operating state. When WAKE_SW is forced logically high,
the RN4020 wakes up and enters Active mode. After
being roused, the RN4020 will send “CMD” to the UART.

ADVANCED TECHNIQUES FOR DESIGN ENGINEERS

2
2
§
&
G
5
=

WS/PIO3MOSI

This signals that the RN4020 is in Command mode and
ready to service commands coming in via the UART.
When the WAKE_SW pin is returned to a logically low
condition, Command mode is exited and “END” is sent to
the UART. The RN4020 will then enter Deep Sleep mode.
The MLDP_EV pin (pin 11) goes logically low to indicate
Deep Sleep Mode. If the UART baud rate is set for 2400
bps, the UART is always accessible and the WAKE_SW pin
does not need to be forced logically high to wake the
RN4020.

The CMD/MLDP pin (pin 8) is used to control the
RN4020 when the radio module is using the MLDP serial
data service. Forcing the CMD/MLDP pin logically high
puts the RN4020 into MLDP mode. In MLDP mode, all
data from the UART is sent to the peer device as a
datastream. This mode is useful for wire replacement
applications. Setting the CMD/MLDP pin logically low will
force an exit of MLDP mode, then the RN4020 returns to
Command mode and sends “CMD” to the UART.

If the RN4020 is in Dormant mode, taking the
WAKE_HW pin (pin 15) logically high will power up the
RN4020. Following the power-up sequence, the RN4020
can be instructed to perform a factory reset. The factory
reset is kicked off by flipping the WAKE_HW pin logically
high, logically low, and logically high three times within
five seconds. If the WAKE_SW pin is logically high during a
factory reset operation, a complete factory reset is
performed. If the WAKE_SW pin is logically low during the
factory reset, a partial factory reset is performed. A partial
factory reset preserves the device name, private service,
and scripts. A private service is any data link configuration
that is not a registered Bluetooth service. For instance,
Microchip’s MLDP is a private service.

M@ Figure 1.The
RN4020 is
small and so is
the pin count.
That's a good
thing since the
more pins we
have to keep
up with, the
more code we
have to write.

02-10303-R3
BUR150218320

@ Photo 2. The PIC18LF25K50 is configured as a USB CDC
device. This configuration allows the RN4020 PICtail to be
attached directly to a PC's USB port. Commands and data
are passed between the RN4020 PICtail and PC using a
simple terminal emulator program.

Pin PIO1 defaults to the CONNECTION LED pin and
will present a logical high when the RN4020 is connected
to a peer device. The MLDP_EV pin is used as an indicator
in MLDP mode, and will go logically high when the
RN4020 must output a status to the UART or requests a
response from the host MCU. Active mode is indicated by
driving the WS pin logically high.

The RN4020 P!ICtail Plus Board

The business end of the RN4020 PICtail is exposed in
Photo 1. As you can see, all of the RN4020’s I/O pins are
accessible via a set of pads surrounding the radio module.
The RN4020 PICtail also includes an onboard 3.3 volt
voltage regulator, a user pushbutton, three status LEDs, an
ICSP interface (J7), and an interface selection jumper (J1).

When jumper J1 is installed, the RN4020 P!Ctail’s
edge connector interface is active. The edge connector
mates with the Microchip Explorer 16 development board
or any other dev board that supports the PICtail or PICtail
Plus footprint. If the jumper at J1 is not installed, the

RESOURCES

ces Microchip
CCS C Compiler RN4020 P!Ctail
www.ccsinfo.com Explorer 16

www.microchip.com

April 2015 NUTS2VOLTS 59

Post comments on this article and find any associated files and/or downloads at www.nutsvolts.com/
index.php?/magazine/article/april2015_DesignCycle.

@ COM48 - Tera Term VT

Fie Edt Setup Control Window Help Mi Screenshot 1.
Rebooting the RN4020 is
one way to get the
coveted "CMD" message.

@ COM48 - Tere Term VT

Fle Edt Setup Control Window Hap Ml Screenshot 2. By simply

entering "+" we can see
Echo On the commands as they are
entered.

P!Ctail falls under the control of a USB-endowed
PIC18LF25K50. The PIC18LF25K50 is shown in Photo 2,
which is a shot of the other side of the RN4020 PICtail
printed circuit board (PCB).

Schematic 1 tells us that the PIC18LF25K50 is acting
as a USB CDC interface that logically links its USB portal
with its UART component. The PIC’s USB portal is
intended to connect to a PC host USB port, while the
PIC’s UART is aimed at the RN4020’s UART interface.
This arrangement allows us to communicate with the

Hi Schematic 1. No rocket science here. This is a
standard PIC18LF25K50 USB implementation.
Note that the PIC has feelers out to all of the
RN4020's control pins.

VUSB
™
R4
4kK7
R5
C4 10k
10nF BT_UART_TX
Js = - vusB VDD3V3
1
D-
5 “a _— —_ "4
=> § BT_UART_RX
USB Mini 8 >
a} wo
N vr
BT_UART_TX

6O NUTS2VOLTS April 2015

RN4020 via a simple terminal emulator like Tera Term Pro.
In addition to the CDC code, the PIC18LF25K50 is loaded
with microcode that exposes an optional PIC18 command
shell that allows us to use a terminal emulator to
manipulate the PIC’s I/O pins.

What's Better than an RN4020
PiCtail Plus Board?

Two RN4020 PICtail Plus boards! Now that we have a
basic knowledge of BLE and the RN4020, let’s put those
back-side USB portals to work and check out what it takes
to build an RN4020 BLE link.

The RN4020 PICtail comes ready to rock at 115200
bps. A proper USB cable is also packed with your new
RN4020 PICtail. Upon plugging in a brand new RN4020
PiCtail and kicking off a Tera Term Pro terminal session, |
was facing a blank terminal emulator window. So, just to
see if the RN4020 was really there, | issued a Reboot
command (R,7 - Enter). The results are shown in
Screenshot 1. The next thing we should do here is make it
a bit easier to see what we’re doing. We can do this by
simply entering “+” and hitting Enter. Screenshot 2 assures

BT_UART RTS
BT_ WAKE
CMD/MLOP.

U2
PIC18LF25K50-I/ML

VDD3V3
R6
MCLR/VPP/RE3 MCLR
PGD =
RB?
PGC
PIO
PIO2

oa oi of -
r i. | nS |
2)
5
&
Ww
a | 3g
22 gz
voB3v3

CL. COMME ~ Tere Term VE

BTA=@01EC@1B279F iin
Name=RN4620 279F
Role=Peripheral
Connected=no

Bonded=no

Server Service=80000000

pher i]
ted=no
aBonded=no

soervel

BH Screenshot 3.The
RN4020 BLE radios
have been reset to
factory defaults using
the command SF,2.

COMMS IML LIS00 pila mtie

that our simple command was executed.

| issued the D command to obtain the contents of the
Tera Term Pro and serial I/O monitor windows you see in
Screenshot 3. Both of the RN4020s have been rebooted
and reset to default factory settings. At this point, both
RN4020 PICtails have the WAKE LED illuminated. As
you've probably already figured out, we have a couple of
RN4020 PICtails and there is a BLE link in our future.

Note that both of our RN4020 PICtails are
unconnected/unbounded peripheral devices. To form a
BLE link, we will need to configure one of these RN4020s
as a central. Let’s make the radio attached to the CCS C
compiler serial 1/O monitor the central; we’ll call it
“Central.” To make that name stick, we must issue the
command S-,Central. Let’s make the RN4020 attached to
Tera Term Pro the peripheral and call it “Peripheral.” Our
work is checked in Screenshot 4.

Now, let’s turn our attention to the central BLE radio
which really isn’t configured to be the central yet. Let’s
draw the king’s sword and knight the RN4020 attached to
the serial |/O monitor. In our case, the king’s sword is the
SR (Set Features) command. The argument of the SR
command is a 32-bit bit mask. Here’s the lowdown:

0x80000000 - Start the connection as a central
0x10000000 - Support MLDP
0x02000000 — Enable UART Flow Control

So, our command to create a central that supports
MLDP with UART flow control is SR,92000000. A reboot
(R,7) is required following the SR command. We can leave
the Server Services (command SS) alone for now as its
default argument of 0x80000000 is quite alright for us.

2 COMME! Tera Tere VT - - —

BTA=0801EC81B279F
Name=Peripheral_279F

Role=Peripheral :

> Sart ect Dutoet Mortar
Connected=no —
Bonded=no
Server Service=80000000

@ Screenshot 4.
Giving the RN4020s
human-readable
names is easy.

mA @orr

| | COMMA ar BES20e ROCHE Mac)

We now have a central. So, let’s configure the
RN4020 attached to Tera Term Pro as the peripheral. As

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you would imagine, the command sequence to produce a
peripheral pawn is very similar to that of the central. The
bit mask forms up like this:

0x20000000 — Auto Advertise
0x10000000 - Support MLDP
0x02000000 - Enable UART Flow Control

The command SR,32000000 plus a reboot will enable
our peripheral RN4020. Since only politicians say “trust
me,” I’d rather produce the real proof like what you see in
Screenshot 5.

We are ready to attempt a connection. The central is
set up to scan for advertisements from the peripheral on
command. The peripheral knows to start advertising on
power-up. With that, we should be able to issue the F
(Start Scanning) command at the central and locate the
advertising peripheral RN4020 node. According to
Screenshot 6, we found an RN4020 peripheral node. A
peek at the BTA (Bluetooth Address) tells us that this is
our peripheral node, which again is called Peripheral. The
BTA is also referred to as the MAC address. To stop the
scanning, we issue the X (Stop Scan) command which is
obscured by an AOK response in Screenshot 6.

Once the scanning has ceased, we can proceed to
connect to Peripheral by issuing the F (Establish
Connection) command. The E command syntax is also
overwritten in Screenshot 7. So, here’s what was entered
in the serial |1/O monitor terminal emulator window:

E,0,001ECO1B279F

BTA=001EC@18279F
Name=Peripheral_279F
Role=Peripheral
Connected=no
\Bonded=no PT tee ectgearen
Server Service=89900080 ao gv

|| MB acceso Breese

| > Seritl Irgnsv Crepe Mower

@ Screenshot 5. As
you can see, we've
configured the

| RN4020 nodes to
match their given

| names.

@orm @rco @arts
9a) 12590)

@ct @rxp

Roce M3c1

62 NUTS2VOLTS April 2015

The zero following the command identifies the
following MAC address as public instead of random. The
WAKE and CONN LEDs on both the central and
peripheral RN4020 nodes are illuminated. Now what?

Since we don’t have an application in place, this is a
good time to test drive MLDP. We can invoke MLDP
mode by simply entering the command / at the central.
Once MLDP mode is active, the peripheral will
acknowledge the mode change and follow the lead of the
central. Messages can then be sent between the nodes in
streams as shown in Screenshot 8. The central message
welcomes the peripheral to MLDP. The peripheral RN4020
must have some kin folk in Tennessee. The peripheral’s
answer is straight out of the Grand Ole Opry and Minnie
Pearl’s mouth.

RN4020 How-To

To continue on with the RN4020, you will need to
have some BLE 4.0 devices available to you. Microchip has
provided demo code for both BLE-equipped Android
devices and their associated PlC-based peripherals.
However, you already have enough to get started on your
own.

For instance, you can use the CCS C compiler to help
you. Let’s “wake up” the RN4020:

output_high (PIN WAKESW) ;
Now that the RN4020 is awake, let’s perform a

factory reset and give the RN4020 some time to get its act
together:

BTA=001EC01B279F
Name=Peripheral_279F
Role=Peripheral
Connected=no
Bonded=no ic
Server Service=80000000 a0 Bex

io Acc Sere 3 HER Send

| > Serial iret Dugeat Monitor

Hf Screenshot 6.
Issuing the F
command begins a
scan operation that is
searching for
advertisements from
peripherals. To stop
the scan, we must
issue an X command.
We've done just that
in this capture.

ante

ance

@ocn mort arm @exh

printf (‘“SF,2\r\n");
delay_ms (500);

We'll make this RN4020 node the central. Before we
make that official, let’s give it an appropriate name:

printf (“S-,IamCentral\r\n”) ;

Okay. Now, let’s sign the papers that declare this
RN4020 node a central, give it MLDP powers, and UART
flow control support:

printf (*“SR,92000000\r\n”) ;
Don’t forget to reboot:
printf(“R,1\r\n"”);

| think you get the idea. Using the RN4020 P!Ctail,
you can “emulate” all of the actual embedded commands
that you would issue using a PIC. You can retrieve
messages from the RN4020 using either a polling method
or interrupt routine. If you only need to capture single
character sequences, the CCS C compiler’s kbhit function
can be used in your RS-232 receive routines.

For those applications where you can’t afford to miss
a character or the characters are coming in while you’re
out plowing the North 40, this code might be useful:

et he i ee eel

ass USART DEFINITIONS
TR KK KK KKK RR Ak AA AA AAA kA OA He

BTA=601EC@1B279F
Name=Peripheral_279F
Role=Peripheral
Connected=no
Bonded=no ———————

Server Service=80000000 -= Bs :
Connected x! (}
~ ASCE Gena Ui Ee Gon Oran Vrweee: ascac

> Serial Inge Outget Mantor

H Screenshot 7. We are
connected!!

#define USART RX BUFFER SIZE
#define USART RX BUFFER MASK
( USART_RX BUFFER SIZE - 1
[ RxBuf [USART_RX BUFFER SIZE];
[ RxHead, USART_RxTail;

unsigned int8 USAR'
unsigned int8 USART

#INT_RDA
void RDA _isr (void)
{

unsigned char data;
unsigned char tmphead;

//read the received data

data = getc();

//calculate buffer index
tmphead = ( USART RxHead + 1
USART_RX_ BUFFER MASK;

//store new index

USART_RxHead = tmphead;
//nandle buffer overrun
if ( tmphead == USART RxTail )

{
CREN = 0;
CREN = 1;

USART_RxTail = 0x00;
USART RxHead = 0x00;

}

// store received data in buffer
USART_RxBuf [tmphead]

\BTA=001EC61B279F
Name=Peripheral_279F
Role=Peripheral
Connected=no
Bonded=no

Server Service=88000000

Connected
MLOP
Welcome to MLDP

M Screenshot 8.

These messages

| were generated by

| typing into the
terminal emulator
window. The
central sent a
welcome message
and the peripheral
replied in the
fashion of Minnie
Pearl.

@ Send 3.10041 Montes

April 2015 NUTSVOLTS 63

et he ee ee eel

1 f* RETRIEVE A CHARACTER FROM USART
et he ei ee ee ee eel

unsigned int8 recvchar (void)
{
unsigned char tmptail;
/* wait for incomming data */

while ( USART_RxHead == USART RxTail );
/* calculate buffer index */
tmptail = ( USART_RxTail +1) &

USART_RX BUFFER MASK;
USART_RxTail = tmptail;
/* store new index */

return USART RxBuf[tmptail];
/* return data */
}

et ee ei ee eal

i f* CHECK FOR CHARACTER IN RING BUFFER
et he eee ee nl

unsigned int8 CharInQueue (void)

{
return (USART RxHead != USART RxTail);

The interrupt code I’ve listed can buffer up to 256
incoming characters at 115200 bps. To check for a
character in the buffer, call the CharlnQueue function. If
the CharlnQueue function returns a TRUE, use the
recvchar function to remove a byte from the buffer. Assign
a UART to the interrupt routine using the #use RS232
preprocessor:

#use rs232 (baud=115200, parity=N,
xmit=PIN C6,rcv=PIN C7,bits=8)

The RN4020 PICtail is a great way to get started with
your own scratch design. In addition to the edge
connector, you can get at the RN4020 using the PICtail’s
male header pins.

This makes the RN4020 available to you via a
perfboard, which makes it super easy to add the RN4020
to your Design Cycle. NV

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PRACTICAL 3D PRINTING

3D Printed
Custom Storage
Boxes

started with a design from Thingiverse.com and

imported it into Tinkercad design software (which is

free at Tinkercad.com). | then went to work making
drawers that fit what | wanted. My thought was to make a
box to contain all the parts for one design. Then, when |
want to build that design, | could just pull out the box and
go to work.

The first box | created held leaded devices like
resistors and capacitors, but it could just have easily held
strips of surface-mount components. The difference was it
took up way less space and | could print any arrangement
| wanted. Because the boxes were so small, | could glue
them together for even more customization. | had one
larger parts drawer that | purchased at Home Depot and
stored all the parts to build a few Microchip PIC based
CHIPINO modules, but the size was far larger than |
needed. So, | decided to create custom drawers that could
hold everything from the circuit board all the way down to
the individual LEDs and 1/8 watt resistors. When | was

lm BY CHUCK HELLEBUYCK

3D printers are the wave of the future — or so countless
articles, reviews, breathless news commentators, and, of
course, the machine’s manufacturers keep telling us. By
now, we've all seen a plethora of itty-bitty cubes, Yoda
heads, chess pieces, interlocking gears, and other
interesting but ultimately useless "things" created with
3D printers. Though many of these little demo pieces are
impressive by themselves, they never quite cross over
into the realm of *useful.* As we believe the "what is
3D printing" topic has been done to death, we thought it
was high time to bring you a useful series on how to
actually implement 3D printing. Specifically, working
with 3D printers and showing you how to use them for
practical projects on your workbench.

@ FIGURE 1.
Resistor box.

done, it saved an incredible amount of space.
The purple box shown in Figure 2 contained four
different drawer layouts. | was able to fit enough

April 2015 NUTS2VOLTS 67

REAL WORLD USES FOR THE ELECTRONICS EXPERIMENTER

divided into two sections. | then made a
four-section drawer that held some of the
larger components. The final two drawers
had five sections each to hold resistors,
diodes, regulators, capacitors, and many
other parts. In the end, all the parts were
contained in one small box with five
drawers.

The other advantage to this setup was |
could customize the box for more drawers
or wider drawers as needed because |
owned the files and could print anything |
needed on my printer.

| could also use a little super glue (or
better yet, acetone) to fuse the boxes
together to make my own custom size set
of drawers. If | need one large drawer, |
could do that too. If | need a handy way to
carry the boxes instead of gluing them
together, | can get a wood case like the one
in Figure 4 that | picked up from Michael's
craft store for $4. It has handles on the side
for carrying, and large openings for drawers.
| 3D printed some large drawers that fit the
bottom row and then put the small box of
drawers in the upper slots. This way, | could
keep designs stored away in an organized

components in the drawers for at least five CHIPINO manner, rather than just components.

modules. This is only limited by your imagination because you
Figure 3 shows some of the drawers. One held just can customize the storage boxes any way you want once

the circuit board, while the larger 28-pin PIC16F886 and you have a 3D printer.

28-pin DIP sockets were in a separate drawer that was Another option is to 3D print the part number in the

bottom of the box. That way, when
the slot is empty, you know exactly
ARLCD 3.5-inch Arduino GPU Combo Just $99.00 twas Wal ices You could us put

a paper note or sticker in the bottom
instead, but 3D printing the part
number is free and it will never get
lost.

Now, add to this all the screws,
nuts, and stand-offs you may have in
your collection of electronic
components. If we used those large
box drawers for all the various
components, we’d have more boxes
than space. Because of that, | have all
the hardware collected in one
drawer. Then, | have to sort through
it to find the part | need.

Being able to quickly build a
custom drawer size that is much
smaller allows me to organize the
various hardware and take up less
space.

Product Specifications: 3.5" color TFT LCD « 320 x 240 Resolution « 65k
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dimensions: 3.x 3 x 9 inches ¢ 6-9V operating voltage * Extremely low
power - draws less than 200m/ « ARLCD Arduino GUI Library ¢ Arduino
UNDO RS Compatible

68 NUTSEVOLTS April 2015

Post comments on this article and find any associated files and/or downloads at www.nutsvolts.com/
index.php?/magazine/article/april2015_Practical3DPrinting.

| can also use different color
plastics to make the drawers and
boxes. Red can be resistors, blue
for capacitors, black for hardware,
etc. The options are endless.

I’ve gotten to the point where |
spend half my time sorting through
all the various storage containers
and boxes that hold my large
collection of electronic parts rather
than building electronic projects.
So, over time, | hope to 3D print a
whole new storage system for my
lab. It should take up a whole lot
less space.

| put my original drawer design
up on my Thingiverse account so
anybody can download the files
and print them. | also made the
designs public on Tinkercad so
anybody can modify them to fit
their specific needs.

| have a YouTube video showing other 3D print
projects. You can see them at www.youtube

.com/user/beginnerelectronics.

@ FIGURE 4. Wood storage box from
Michael's craft store.

If you have a 3D printer question
or project idea, send me an email at

chuck@elproducts.com and I'll try to
help. NV

Resources

Check out my website and blog:
www.elproducts.com

Check out my

YouTube Channel:
www.youtube.com/user/beginner
electronics

Check out my 3D designs:
www.thingiverse.com/
elproducts/designs

Tinkercad:
www.tinkercad.com

da Vinci 3D:
us.xyzPrinting.com

da Vinci Forums:
www.solidforum.com
www.voltivo.com

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April 2015 NUTS2VOLTS 69

NEAR SPACE

mi BY L. PAUL VERHAGE

CubeSats — Part 3:
Attitude and Velocity

Attitude refers to the orientation
of a spacecraft in space. The first
spacecraft, Sputnik 1 didn’t maintain
an attitude at all; it just tumbled as it
orbited earth. Some spacecraft, on
the other hand, were intentionally
spun during launch like America’s
Explorer 1. The spin imparted an
angular momentum that prevented
the spacecraft from tumbling.

Some spacecraft maintained their
attitude in three axes using systems
like thrusters (this is called three-axis
stabilization). Examples of three-axis
stabilized spacecraft include the
Voyager 1 and Voyager 2.

70 NUTS2VOLTS April 2015

Announced last year, the Jet Propulsion Laboratory is
planning to test two university-built CubeSats on a
mission beyond earth orbit. The mission is called
INSPIRE — Interplanetary NanoSpacecraft Pathfinder
In Relevant Environment — and includes the
University of Michigan, Ann Arbor, Cal Poly San Luis
Obispo, and the University of Texas at Austin.

f

Methods to maintain stabilization

are only half the story, however. A
spacecraft must first determine its
orientation in space. Although this
article has broken these systems into
two parts — attitude control and
attitude determination — satellites
combine the two operations into a
single subsystem called the Attitude
Determination and Control System
(ADCS).

CubeSats need an outside
reference in order to determine their
attitude. Outside references include
things like the earth’s horizon, the
sun, stars, and earth’s magnetic field.
Sun sensors are conceptually simple;
they’re circuits that determine how

closely a surface faces into the sun.

The shortcoming is that a sun
sensor can only provide a position
along a single axis in space.

APPROACHING THE FINAL FRONTIER

Post comments on this article and find any associated files and/or downloads at
www.nutsvolts.com/index.php?/magazine/article/april2015_NearSpace.

Therefore, a CubeSat carrying only a
sun sensor could be rotated at any
angle along the axis connecting the
CubeSat to the sun and the CubeSat
would not know. To increase attitude
knowledge, a second or even third
attitude sensor is sometimes
incorporated into the CubeSat.

By using an imager, a sun sensor
permits software to determine its
offset from the sun in terms of a
vector (magnitude and angle). To
ensure the sun sensor only detects
the sun, there’s a neutral density filter
over the sun sensor’s imager that’s so
dense that only sunlight can reach it.

CubeSats in earth orbit can use
earth itself as the second reference

Magnetometers can be
pretty simple devices
because of today's
electronic technology.
This one is an
engineering model of
the MiniMag 3.

Weighing only 3/4 lb, the BCT Nano Star
Tracker only occupies a quarter of the
volume of a 1U CubeSat while only

point. The earth sensor measures the
position of earth’s horizon with
respect to the CubeSat. That’s made
possible because there’s a huge
difference in temperature between
the warm earth and cold space. By
measuring the position of earth’s
horizon (in infrared), a CubeSat
knows the location of the horizon
with respect to the CubeSat and
therefore the nadir (straight down to
the earth).

Earth-orbiting spacecraft
(including CubeSats) can rely on
magnetometers as another tool for
determining their attitude. This means
magnetometers are less effective the
farther from earth the CubeSat orbits,
and they’re useless for interplanetary
missions. If a magnetometer is being
used for attitude determination, it’s
important that there be no distorting
magnetic fields associated with the
CubeSat. The fields can confuse the
magnetometer and result in a bad
attitude determination.

Two ways to get around this
issue are to either place the
magnetometer on the end of a boom
that’s a good distance away from the
magnetically dirty spacecraft, or to
determine the magnetic environment
of the CubeSat and then subtract this
as background noise from the
magnetometer’s signal. The second

consuming 3/4W of power. A CubeSat

option is made more
difficult by the changing
magnetic environment of
the CubeSat that results
from systems and sensors being shut
on and off.

One of the more interesting
techniques for attitude determination
is the star sensor. Simple ones were
used as far back as 1964 for the
Mariner 4 mission to Mars. Today,
star sensors are not just for NASA
and ESA spacecraft. Blue Canyon
Technologies makes a Nano Star
Tracker that determines the attitude
of a CubeSat in three axes by
comparing the images of star fields
that it sees to a catalog of stored
stellar positions. By identifying fields
of stars, the software can determine
the pointing direction and rotation of
the CubeSat. Now, that’s pretty cool.

CubeSat
Attitude Control

Once a CubeSat’s attitude is
known, it can apply forces to change
it to the desired attitude. Two popular
ways CubeSats control their attitude
are through magnetorquers and
reaction wheels. Thrusters are also
possible, but that requires propellant
which can be in limited supply or
non-existent in CubeSats.

carrying one of these will know its attitude

in space to less than one degree.

Magnetorquers

Because of earth’s native
magnetic field, CubeSats in earth
orbit cannot only determine their
attitude with reference to it, they can
also use it to change their attitude in
space.

CubeSats can use magnetorquers
or coils of wire wrapped around
metal rods to push and pull on
earth’s magnetic field. Applying a
current to a magnetorquer generates
a magnetic field that interacts with
earth’s magnetic field. When the two
fields don’t line up, the misalignment
creates a torque on earth and the
CubeSat according to Newton’s Third
Law of Motion. Since the CubeSat is
far less massive than earth, the
CubeSat’s orientation changes
significantly while earth’s doesn’t. In
other words, a CubeSat behaves like
a compass needle.

CubeSats can carry two or three
perpendicular magnetorquers to hold
their attitude at precise angles. A
magnetorquer is a great method to
change the orientation of a CubeSat
since it allows it to change its attitude

April 2015 NUTS#VOLTS 71

paul@nearsys.com

An example of two perpendicular
magnetorquer rods. This particular example is
from Delfi Space and will be used by the
CubeSat to dump excess momentum. Delfi
Space is the CubeSat program of Delft
University of Technology (yeah, go Dutch!).

frequently without consuming
propellant. Its weakness is that they
still permit a CubeSat to spin along a
magnetic field line.

Reaction Wheels

Reaction wheels are even better
at holding a CubeSat attitude. They
are motor mounted masses that are
spun forwards or backwards.
According to Newton’s Laws, when
an internal mass rotates, the CubeSat
to which the motor and weight are
attached spins in the opposite
direction. That also means if a
CubeSat is already spinning, a
reaction wheel can slow that spin
down by imparting a spin in the
opposite direction on the CubeSat.

To control the spin and
orientation of a CubeSat along three
axes, three reaction wheels are
installed into the CubeSat — each
with its spin axis perpendicular to the
other two. A fourth reaction wheel
with a spin axis equidistant from the
other three reaction wheels can give

72 NUTS2VOLTS April 2015

a level of redundancy
in case one wheel fails.
There comes a
time when the reaction

wheels may be
spinning at their highest
designed speed. When
that happens, the wheels become
saturated with momentum and must
be desaturated to be of any further
use. A method used to desaturate
reaction wheels is to slow them
down by transferring momentum to
the CubeSat. Then, the CubeSat
applies the magnetorquers in order
to reduce the CubeSat’s spin.

Changing CubeSat
Velocity

| came across two interesting
ways that CubeSats change their
velocity: through the use of
propulsion systems and braking
systems

Propulsion

Among the many important
factors of propulsion systems, two
factors stand out: a given engine’s
efficiency and the total amount of
velocity change possible. Specific
Impulse (Isp) is one measure of the
fuel efficiency of a propulsion system.

A reaction wheel for CubeSats.
As the wheel spins, the
CubeSat spins in the opposite
direction (according to
Mr. Newton).

The unit of Isp is the
second and it calculates the
force generated by a
propulsion system by
multiplying the engine’s Isp
___ by the rate of propellant
flow.
\ For example, an engine
with an Isp of 100 seconds
_ that consumes two pounds
of propellant per second
generates 100 seconds * 2
pounds/second, or 200
pounds of thrust. For
comparison, black powder
model rocket engines have
an Isp between 70 and 100
seconds, while the Space
Shuttle Main Engines
(SSME) have an Isp of over
400 seconds in a vacuum.

Changes in velocity are often
referred to as delta-V (AV). The
maximum amount of AV possible is
one factor in a spacecraft’s useful life,
and it depends on both the engine’s
efficiency and the amount of
propellant carried by the spacecraft.
What one notices about Isp is that
the lower an engine’s Isp, the more
propellant a satellite must carry to
achieve its desired maximum AV.

Because of a CubeSat’s small
volume and mass, its propulsion
system must have a high Isp if it is to
be able to affect the CubeSat’s orbit
in a serious way. The most efficient
engines are those with the highest
exhaust velocities which can be
related to the temperature of the
exhaust.

With specific impulses measured
in the thousands of seconds, ion are
the best engines we have for
interplanetary travel. Since ion
engines are stingy when it comes to
propellant flow, they’re unable to
generate large amounts of thrust and
are therefore incapable of launching
rockets from the surface of a planet.

| found an ion engine for
CubeSats called a pulsed plasma
thruster (PPT) that’s sold by Clyde
Space, and has an Isp of 608
seconds. According to their website,

this engine can double the orbital
lifetime of a CubeSat in some cases
(the extension depends on the height
of the CubeSat’s orbit).

In high altitude orbits where the
air density is low, a PPT only requires
0.04 watts of power to counteract
the effects of air drag. In a lower
earth orbit, the increased air drag
means a CubeSat carrying a PPT
needs to expend over two watts of
power to overcome the effects of
drag.

Another CubeSat propulsion
system is the resistojet. Surrey
Satellite Technology Ltd (SSTL) sells a
resistojet consisting of a hot wire in
which a liquid propellant is forced
into contact with it. As the liquid gets
hot, it vaporizes and creates thrust.

What kinds of propellant are
used? The propellant used in the
Surry Training, Research, and
Nanosatellite Demonstrator
(STRaND-1) CubeSat uses butane as
its propellant. The system is called
BPS for Butane Propulsion System
and has an Isp of 90 seconds. With
the amount of propellant available
and the design of the resistojet,
STRaND-1 can change its velocity by
a total of two meters per second.

Braking Systems

| found another interesting
product for CubeSats: braking sails. A
concern for the astronautics
community is the risk to expensive

An artist impression of the Aerodynamic End
Of Life Deorbit System for CubeSats doing its

thing. The sails are folded up inside a
module attached to a CubeSat. At the

appropriate time, the sails deploy out from

the CubeSat.

This artwork by the University of Michigan depicts a test of the ion

engine they are designing. This engine uses permanent magnets in
order to reduce the power requirements of the engine.

satellites that a boom of CubeSat
launches could create. Orbits
crowded with large numbers of
inexpensive CubeSats create collision
risks and no one with a $20 million
satellite wants their hardware
damaged by a $20,000 CubeSat.
One way to mitigate this risk is to
place CubeSats into low earth orbits
(LEO) that decay after a year or two.
A second way is to install braking
systems on CubeSats.

The orbital lifetime of a
spacecraft depends on its size, shape,
mass, and altitude of its orbit. The
lowest orbiting CubeSats remain in
orbit for less than a
week, while higher
altitude ones can remain
in orbit for over five
years.

Once a CubeSat has
completed its mission,
there’s usually no reason
for it to remain in orbit.
Therefore, an end of life
system to return
CubeSats back to the
atmosphere in a
destructive manner fills
an important need.

Clyde Space is

thin

creating AEOLDOS, or Aerodynamic
End Of Life Deorbit System for
CubeSats as a way to remove
CubeSats from orbit. AEOLDOS is a
system to de-orbit CubeSats, as Clyde
Space puts it. It acts like the reverse
of a solar sail.

Instead of using solar radiation
pressure to propel a CubeSat, the
braking sail increases the surface area
of a CubeSat in order to slow it
down. The increased surface area
increases the drag that the
atmosphere imparts to the CubeSat.
The lower the CubeSat’s altitude, the
greater the density of earth’s
atmosphere and the greater the drag
created by the sail. The braking sail
will remove a CubeSat from orbit
much more quickly than it would
otherwise.

This was a brief discussion about
attitude control and change of
velocity systems available for
CubeSats. Next time, I’d like to
acquaint readers with some of the
CubeSat programs out there. You'd
be surprised to learn where some
people want to send CubeSats.

Onwards and Upwards,
Your near space guide NV

April 2015 NUTSVOLTS 73

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m NEW
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Continued from page 47,

The receiver
architecture is that of a
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hetrodyne receiver that is
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SSB, or CW.

The receiver
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Other front panel
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READER-TO-READER

ECHFOR

>>> QUESTIONS

LED vs. Incandescent Lamps

| have been tasked with the chore
of replacing 300 watt incandescents
(5900 lumen). How many of what
kind of LEDs and current-limiting
diodes in series/parallel do | need to
fool the human eye into thinking it is
seeing a brighter, more pleasant level
of lumens?
#4151 James McFadden

St. Maries, ID

Test Lead Wire
Anyone know where | can pur-
chase small quantities (25 ft rolls) of
the different color jackets of good
Beldon or (?) 65/30 test lead wire? |
see it in 100 ft rolls $$, 10 colors, but
that would be over a $1,000 for all ten.
#4152 Terry Arnall
Hayward, CA

Over Current for PWM Circuit

| have a Marlin P. Jones DC motor
speed controller (Part 31566MD, 6-24
volts, 20 amps max). | need to add an
over current circuit to it. | inserted two
0.1 ohm/five watt resistors in series
with the motor -lead and the M-con-
nection on the controller. My scope
displays a steady 0.6 volts DC level
across it. The PWM _ waveform
changes from 2 usec to 40 usec in
length as the output of the speed con-
troller is increased from O to 3 amps,
while my DVM displays 0.02 VDC to
1.3 VDC for the same range of output.

So, the question is “What kind of
circuit can | add across the resistors to
get a VDC reading?” | have tried an
NPN transistor, base lead to the motor

All questions AND answers are
submitted by Nuts & Volts readers and
are intended to promote the exchange
of ideas and provide assistance for
solving technical problems. All
submissions are subject to editing and
will be published on a space available
basis if deemed suitable by the
publisher. Answers are submitted

78 NUTSEVOLTS April 2015

-lead, and the emitter lead to th
connection. (With a 10K collector
resistor to +12 VDC.) The collector
voltage went from +12 volts to +3
volts as the controller output went
from 0 to 3 amps.

Next, | connected the collector
voltage to an LM324N quad op-amp
set up as a voltage comparator. The
tlead of an LM324 went to a 200K
pot, connected between +12 VDC
and Gnd. The transistor’s output went
to the -input of the same op-amp. A
1M ohm resistor is connected from
output to tinput for hysteresis. (This
output should go high to set a
CD4013N flip-flop at an over current
condition.)

The problem is that the output of
the op-amp’s output does NOT
change at the point when the voltage
at the +input is greater than the
-input. The op-amp’s output changes
as the voltage from the transistor
decreases. | used the LM324N auad
op-amp because it has four op-amps in
one chip, and it works with a single
+12 VDC supply. It would be helpful if
the new circuit could use it also, but
not necessary. I could use a
PIC16F628 or an Arduino Nano, if you
design with them.
#4153 Patrick Fleming
Hoffman Estates, IL

>>> ANSWERS

[#12145 - December 2014]
False Readings

| bought one of those Internet-
aware soil moisture devices a few
months ago. It worked great at first, but
now the electrodes are oxidized and

by readers and NO GUARANTEES
WHATSOEVER are made by the
publisher. The implementation of any
answer printed in this column may re-
quire varying degrees of technical
experience and should only be
attempted by qualified individuals.

Always use common sense and
good judgment!

because of
ubbing the
electrodes with steel wool works for
about a week. Any ideas for a
permanent solution?

If the sensor is powered with a
direct current voltage, you may be out
of luck. However, here are some pos-
sible 'fixes.'

| read that the phone company,
many years ago, had a problem with
corrosion and switched from a nega-
tive ground to a positive ground which
helped to solve their corrosion prob-
lem. If you could insure the system is +
grounded, this may help.

| think that most serious outside
systems use AC sensors, and if they
use DC, employ a positive ground and
are not powered unless a measure-
ment is needed.

Marc Forgey
Seattle, WA

[#3151 - March 2015]
X10 Cable Build

| have an early X10 Home Control
Timer (Model CP-290) to which I have
lost the programming cable. Does
anyone know where | can get the
pinout so | could fashion my own
replacement cable?

The CP-290 is very old and was
sold in the early 1980s. The
communication protocol is RS232
serial.

Baud Rate: 600

Data Bits: 8

Parity: None

Stop Bits: 1

The connector on the back is a
standard five-pin DIN socket. Looking
at the back of the unit, the pins are 5-
4-3-2-1, starting at the left and going
counter-clockwise to the right with pin
5 on the left, 3 on the bottom, and 1
on the right.

Pin 1 - No Connection

Pin 2 - Receive Data (In)

>>>YOUR ELECTRONICS QUESTIONS ANSWERED HERE BY N&V READERS

Send all questions and answers by email to forum @nutsvolts.com
or via the online form at. www.nutsvolts.com/tech-forum

Pin 3 - Ground
Pin 4 - Transmit Data (Out)
Pin 5 - No Connection

To plug into a computer like an
IBM compatible these connections
would go to a nine-pin female serial
connector:

CP290 + DE9

2 RxD > 3 Txd

3 Gnd > 5 Gnd

4 TxD > 2 RxD

Rick Swenton
via email

[#3152 - March 2015]
Lightning Protector

In a recent thunderstorm, a nearby
lightning strike took out some of the
electronics at my neighbor’s house. Is
there anything a DlYer like me can
build to protect my _ delicate
electronics — other than unplugging
everything? Something with MOVs
maybe?

#1°~ Lightning protection is a
complex issue, including home
entrance cable protection, bonding of
large metallic structures, and even
grounding of rain gutters and
downspouts. A good place to start is a

free PDF from www.lightningsafety

.com/nlsi_lhm/IEEE_Guide.pdf.

Because a lightning bolt can pack a
500 MJ wallop — far beyond any MOV
rating — surge protectors are not
protection against a direct strike, but
they do help limit inductive surges
(e.g. lightning hitting a tree nearby,
inducing a current in house wiring). In
brief, running a hefty ground wire
from gutters, external antennas, etc.,
to an effective ground in conductive
soil is the first line of defense.

MOV surge suppressors have
saved my PC and appliances from one
damaging surge — as shown by blown
internal fuses and smoking MOVs!

B. Bresnik
via email

#2 The simplest solution to
lightning-induced surge protection is
to use a commercially available surge-
protected outlet strip. There are
numerous sources for these items, and
you may even find a suitable device at
your local hardware store.

The important thing to understand
is that a lightning strike conducts huge
oscillatory currents. A varying
electrical current will generate a
changing magnetic field which, in
turn, will induce superimposed
voltages in nearby conductors -
including service drops from the utility
pole to your house (e.g., electrical
power, TV/Internet cable, and
telephone). Such surges can be
induced both line-to-line and line-to-
ground in the electrical power service
drop (and for — balanced-line
applications such as_ telephone).
Properly designed surge suppressors
provide both line-to-ground and line-
to-line protection for such circuits.

Surge voltages induced _line-to-
ground arise because such devices
often are connected to more than one
source of surge voltage. For example,
your television set is connected to
utility power and also connected to
the TV signal cable. Likewise, your
computer may be connected to utility
power, to a cable from your Internet
service provider, and to a telephone
cable (for fax service). Unless these
cables/wires are all run together

throughout the house (and_ this
practice is discouraged due to the
possibility of capacitive cross-

coupling), one or more loops exist,
and within each loop, the surge
voltage induced by the lightning strike
is a direct function of the areas
enclosed by the loop.

It follows that effective surge
suppression can only be
accomplished by feeding all of the
incoming electrical services through
what is called a "surge-protective
window." In such a structure, surge
suppression elements such as metal

oxide varistors (MOVs), avalanche
diodes, or gas tubes can clamp
impulse voltages to a common
reference point plane which, in turn, is
connected to earth ground. This can
be effected by using a surge-protected
outlet strip that also incorporates
protection for telephone and cable
lines. Typical examples of this all-
inclusive surge protection are devices
available — from Belkin (e.g.,

www.belkin.com/us/BV112234-08-
Belkin/p/P-BV112234-08/) and

Tripp-Lite (e.g., www.tripplite.com/av-

home-theater-surge-protector-isobar-
10-outlets-8-ft-cord-3240-joule-3-line-
coax-ethernet-tel-network~AVBAR10.
/).

All cables exiting the surge
suppressor block should be run
together wherever possible, secured
periodically by twist-ties or other
means. This method ensures that
negligible induction areas exist into
which surge voltages can be
introduced. Capacitive-coupled
interactions are no longer a problem
because any prior surge voltages have
already been stripped from the cables
by the surge suppressor block.

Please note that the protectors
identified above are "Cadillacs"
because they provide surge
suppression for all common power
and media transport — wiring.
Sometimes just a simple one-outlet
surge suppressor will do the job — or,
for example, a single-outlet suppressor
with built-in telephone line surge
suppression — both at significantly
lower cost. | even use single-outlet
surge suppressors to protect my
coffee maker and washing machine
because each of these devices
contains electronic modules that are
expensive to repair.

The important consideration is to
maintain the "surge protective
window" approach to the problem as
outlined above.

Peter A. Goodwin
Rockport, MA

April 2015 NUTSEVOLTS 79

READER FEEDBACK. cxmestnenez

For reproduction parts like
rubber, knobs, dial faces, etc., and
other cosmetic parts, | recommend
Renovated Radios

(www.renovatedradios.com).
J.W. Koebel

Tread Thread

| have a minor correction for
Theron Wierenga’s January 2014
barn door tracker. The article states
that the tread used to mount most
cameras is 1/4-28; it’s actually 1/4-
20.
Arlen Raasch

Arlen, thank you for your
comments. | concur and also
appreciate the heads-up on the typo
about the thread size.

Theron Wierenga

Loves Ham

| absolutely love the addition of
the ham radio centric articles in the
latest volumes of Nuts & Volts. |
think it’s a great way to expose
readers to the technical aspects of
ham radio, of which they may not
know about. Keep up the great
work!

73, Ryan Clarke KJ6MSG

Spaced Out on CubeSats

There are several errors and
omissions in Paul Verhage’s February
2015 Near Space column on
CubeSats. The Pumpkin standard
board is NOT a PC-104 board. The
form factor is a PC-104 size and
shape and the 104-pin connector is
the same, but the signals on that are
entirely different.

If you plug a PC-104 board into
a Pumpkin or similar board, you will
certainly burn up both.

He listed four companies
producing subsystems for CubeSats

8O NUTSZVOLTS April 2015

— the ones with an easy-to-find
website. There are at least 20 that
produce various modules and more
every day.

Paul discussed CubeSat air
frames made from panels or
skeletonized. There are any number
of ways to make the structure of a
CubeSat, and many builders make
their own (often customized), so
their particular sensor or other
subsystem will fit.

There is no end to the creativity
builders have engaged in for
structures. For example, the PrintSat
structure is entirely 3D printed.

Paul also mentioned expansion
and contraction due to temperature
changes as a reason solar panels are
“clipped” to a structure. That’s not
the reason for the clips at all. It’s for
ease of assembly and disassembly.

While the thermal coefficients of
solar cells and aluminum are
different, over the space of 10 cm,
there isn’t enough difference to
create risk for the cells. More often,
the substrate the cells are on is
bonded to or isolated from the
structure to allow heat from the cells
to be conveyed to the structure, or
to keep that heat away from the
structure because a particular
satellite’s thermal budget needs more
heat or less.

There are numerous ways solar
panels are connected to structures;
clips are a minor player in that game,
with nuts and bolts being much
more prevalent.

Li-Po and Li batteries used in
CubeSats were discussed. In reality,
virtually every battery chemistry has
been and continues to be used. The
choice depends on the power needs.
For example, NiCds are still used
when a large amount of current is
needed for a short time.

The only constraints on
chemistry are what the launch
vehicle provider will allow. For the
most part, they will allow anything
because the CubeSat is in a closed
deployer.

Regarding the P-POD deployer
from Cal Poly. There are at least five
companies making deployers now,
with more being invented every day.
Two of the more popular are the ISIS
and Planetary Systems, Inc. NASA
Ames makes its own: the NLAS.

It was indicated that a CubeSat
radio only needs to transmit at a
couple of watts to be heard with a
handheld amateur radio. The
threshold is closer to 100 mw for FM
voice, and less than that for CW.

| was stated that Doppler
correction is necessary. On VHF with
FM, it isn’t. The Doppler shift is only
about 1.2 kHz for a LEO satellite,
and with FM it’s unnecessary to
correct for that. It is, of course, for
SSB.

Jim White

Colorado Satellite Services, LLC

Thanks for the information on the
Pumpkin board. It does have the
appearance and measurements of a
PC-104 board. Therefore, it would be
important to know the function of
each pin so you don't destroy boards
by stacking them together.

As with many products, it's
important to read the datasheets. |
guess it goes to show that what looks
like a standard might not be in all
cases.

| read how NiCds are space
qualified, but wasn't aware they were
still heavily used.

! looked at CubeSats for the first
time several years ago. Since then, it
has indeed grown. | get the feeling
that I'm watching CubeSats grow like
the home PC grew several decades
ago.

It would seem to me that
beginners would be well served
looking at CubeSat kits first and then
expanding out from there.

Paul Verhage

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MIT'S SPRINGTIME }
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your output, and connects easily between your trans- stereo transmitters for more than U
mitter & antenna. Maximum input power is 50 watts. © two decades!
FMLP1 FM Low Pass Filter Kit $25.95 E ; :
— ie Just plug in the stereo left/right audio from your MP3

play CD Pleyel or computer, and broadcast it on any
tequency in the standard FM broadcast band.

Tunable FM Stereo
Transmitter Kit

Here is the famous entry-level kit
that will teach the basics of FM
Broadcast transmission while finding
many uses around the home or dorm
room.

The sound quality and stereo separation of this little
transmitter will keep the pickiest audiophile happy.
The FM25B features a PIC microprocessor for easy fre-
quency programming through board mounted DIP
_ switches. The transmit frequency is Phase Locked
Loop (PLL) controlled for unparalleled stability making
frequency drift a thing of the past, extremely critical for
digital tuners. The RF output level is adjustable from
5uW to 25 mW via a potentiometer. Use the built-in
whip antenna or use an external antenna with the
standard "F" external antenna connector on the rear
panel. Just plug it in and you're on the air.
(Note: The FM25B Is a do-it-yourself learning kit that you assemble.
Please remember that the end user is responsible for complying with
all FCC rules & regulations within the US, or any regulations of their
respective governing body in regards to the application and use of

The FM10C has plenty of power to cover your home,
backyard, or city block and tunes through the entire
88-108MHz band in three separate ranges with a

tuned LC circuit. Runs on a 9V battery or optional AC»
power adapter.

(Note: The FM10C is a do-it-yourself learning kit that you assemble.
Please remember that the end user is responsible for complying with

all FCC rules & regulations within the US, or any regulations of their

respective governing body in regards to the application and use of |
Age FM IOC) J go | the FM25B.)
FM10C FM Stereo Transmitter Kit $39.95 FM25B_ Synth FM Stereo Xmtr Kit $119.95

| The impossible AM radio anten-

© The popular antenna for the serious

~ RF bypass and front panel gain control.

1G7 lon Generator Kit $64.95

HV Plasma Generator

’ Generate 2” sparks to a handheld

screwdriver! Light fluorescent tubes

without wires! This plasma genera- ©

tor creates up to 25kV at 20kHz from a

solid state circuit! Build plasma bulbs from

regular bulbs and more! Runs on 16VAC or 5-24VDC.

PG13 HV Plasma Generator Kit $64.95
= a)
Signal Magnet Antenna , *"*#".

4y1%

na that pulls in the stations and
removes the noise, interference,
and static crashes from your radio! Also
helps that pesky HD AM Radio stay
locked! Also available factory assembled.

SM100 _ Signal Magnet Antenna Kit $89.95

a ==

Broadband RF Preamp

) Need to “perk-up” your counter or

other equipment to read weak sig- “S «
nals? This preamp has low noise and Sas
yet provides 25dB gain from 1MHz to well

over 1GHz. Output can reach 100mW! Runs on

~ 12 volts AC or DC or the included 110VAC PS. Assmb.

PR2 Broadband RF Preamp $69.95
=— —==

Active Receive Antenna

DX’ers works on all bands - shortwave,
HF, VHF, and UHF yet IUDs like a
60’ long wire antenna! Provides over
15dB of gain, and includes auto-off

AA7C Active Antenna Kit $59.95

| There's ont h h ew
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tual electronic catalog! Flip through the Follow us on your favorite network site and quam

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Digital Controlled FM Stereo Transmitter

PLL synthesized for drift free operation

Front panel digital control and display of all set-
tings and parameters!

Professional metal case for noise-free operation
EMI filtering on audio and power inputs

Super audio quality, rivals commercial broadcasts
Available in domestic kit or factory assembled
export versions

For more than a decade we've
been the leader in hobbyist FM radio transmitters. We
told our engineers we wanted a new technology transmitter that would provide
FM100 series quality without the advanced mixer features. They took it as a chal-
lenge and designed not one, but TWO transmitters!

Shemtont
Operaerg Mote

The FM30B is designed using through-hole technology and components and is
available only as a do-it-yourself kit with a 25mW output very similar to our FM25
series. Then the engineers redesigned their brand-new deal using surface

J mount technology (SMT) for a very special factory assembled and tested
FM35BWT version with 1W output for our export only market! All settings can be
changed without taking the cover off! Enter the setup mode from the front panel
and step through the menu to make all of your adjustments. A two line LCD dis-
play shows you all the settings! In addition to the LCD display, a front panel LED indicates PLL lock so you know
you are transmitting.

Besides frequency selection, front panel control and display gives you 256 steps of audio volume (left and right
combined) as well as RF output power. A separate balance setting compensates for left/right differences in
audio level. In addition to settings, the LCD dipiay shows you “Quality of Signal” to help you set your levels for
optimum sound quality. And of course, all settings are stored in non-volatile memory for future use! Both the
FM30B and FM35BWT operate on 13.8 to 16VDC and include a 15VDC plug-in power supply.

(Note: After assembly of this do-it-yourself hobby kit, the user is responsible for complying with all FCC rules & regulations within the US, or any
regulations of their respective governing body. FM35BWT is for export use and can only be shipped to locations outside the continental US or
valid APO/FPO addresses or valid customs brokers for end delivery outside the continental US.)

FM30B Digital FM Stereo Transmitter Kit, 0-25mW $169.95
FM35BWT Digital FM Stereo Transmitter, Assembled, 0-1W (Export ONLY) $259.95
= lp

£lectrocardiogram ECG Heart Monitor

Visible and audible display of your heart rhythm!
Bright LED “Beat” indicator for easy viewing!
Re-usable hospital grade sensors included!
Monitor output for professional scope display
Simple and safe 9V battery operation

Use the ECGIC to astound your physician with your knowledge of ECG/EKG sys-
tems. Enjoy learning about the inner workings of the heart while, at the same time, cov-
ering the stage-by-stage electronic circuit theory used in the kit to monitor it. The three probe
wire pick-ups allow for easy application and experimentation without the cumbersome harness
normally associated with ECG monitors. .
feel
The documentation with the ECG1C covers everything from the circuit description of the kit to the circuit descrip-
tion of the heart! Multiple “beat” indicators include a bright front panel LED that flashes with the actions of the
heart along with an adjustable level audio speaker output that supports both mono and stereo hook-ups. In
addition, a monitor output is provided to connect to any standard oscilloscope to view the traditional style
ECG/EKG waveforms just like you see in a real ER or on one of the medical TV shows! The fully adjustable gain
control on the front panel allows the user to custom tune the differential signal picked ae by the probes giving
you a perfect reading and display every time! Additional patches are available in 10-packs. Operates on a stan-
dard 9VDC battery (not inclu ed) for safe and simple operation. intended for hobbyist usage only. If you experi-

ence any cardiac symptoms, seek proper medical help immediately!

ECGIC Electrocardiogram Heart Monitor Kit With Case & Patches $44.95

ECGIWT Electrocardiogram Heart Monitor, Factory Assembled & Tested $89.95

ECGP10 __Electrocardiogram Re-Usable Probe Patches, 10-Pack $4.95
= — a= =p

Tickle-Stick Shocker 12VDC Regulated Switching Supply

The kit has a pulsing 80 volt tickle Go green with our new 12VDC 1A —

output and a mischievous blink- « regulated supply. Worldwide input

ing LED. And who can resist a 100-240VAC with a Level-V efficien-

blinking light and an unlabeled cy! It gets even better, includes DUAL

switch! Great fun for your desk, “Hey, ferrite cores for RF and EMI suppression. All this F

| told you not to touch!” Runs on 3-6 VDC. * at a 10 buck old wallwart price! What a deal!

TS4 Tickle Stick Kit $9.95 AC121 12VDC 1A Regulated Supply $9.95
— — —_—

Passive Aircraft Monitor 12VDC Worldwide Supply

The hit of the decade! Our patented receiver
hears the entire aircraft band without any tun-
ing! Passive design has no LO, therefore can
be used on board aircraft! Perfect for air-
shows, hears the active traffic as it happens!
Available kit or factory assembled.

® It gets even better than our AC121
above! Now, take the regulated
Level-V green supply, bump the cur-
rent up to 1.25A, and include multi-
ple blades for global country com-
* patibility! Dual ferrite cores!

ABM1 Passive Aircraft Receiver Kit $89.95 PS29 12VDC 1.25A Global Power Supply $19.95
=— —==> = ==

£lectret Condenser Mic Sniff-lt RF Detector Probe

This extremely sensitive 3/8” mic » Measure RF with your standard ~N

has a built-in FET preamplifier! It’s a DMM or VOM! This extremely sensi- ©

a great replacement mic, or a perfect
answer to add a mic to your project.
Powered by 3-15VDC, and we even include coupling

cap and a current limiting resistor! Extremely popular!

MC1 Mini Electret Condenser Mic Kit $3.95

GET THE iNUTS2VOLTS DISCOUNT!

Mention or enter the coupon code

tive RF detector probe connects to

any voltmeter and allows you to meas-

ure RF from 100kHz to over 1GHz! So sensitive it can
' be used as a RF field strength meter!

RF1 Sniff-It RF Detector Probe Kit $27.95

800-446-2295

£lectronic Chirping Cricket Sensor

~

Electronic cricket? Sounds
just like those little black
critters that seem to
come from nowhere
and annoy you with
their chirp-chirp! And
just like the little critters,
we made it sensitive to
temperature so when it gets warmer, it chirps faster!

That's right, you can even figure out the temperature
by the number of chirps it generates! Just count the
number of chirps over a 15 second interval, add 40,
and you have the temperature in degrees Fahrenheit!
Not as fancy as a digital thermometer but much more
unique! And unlike its little black predecessor, the
ECS1 operates from around 50°F to 90°F! | don’t think
there are too many real crickets chirping away at 90°F!

A unique thermistor circuit drives a few 555 ICs pro-
viding a variable chirp that is guaranteed to annoy
everyone around you! But just watch their faces when
you tell them the temperature outside! Runs on 9-
12VDC or a standard 9V battery (not included).

Includes everything shown, including the peat and
battery clip, to make your cricket project a breeze.
ECS1

Electronic Cricket Sensor Kit $24.95

Fun Electronic Learning Labs

Learn and build!

130, 200, 300, & 500 in one labs!

Practical through hole and SMT soldering labs!
Integrated circuit AM/FM radio lab!

Super comprehensive training manuals!

Starting out our “All in One” series, the PL130A, gives
you 130 different electronic projects, together with a
comprehensive 162 page learning manual. A great
start for the kids...young and old! Next, check out the
PL200, that gives you 200 very creative and fun proj-
ects, and includes a neat interactive front panel with 2
controls, speaker, LED display and a meter. From
there, step up to our PL300, which gives you 300 sep-
arate electronic projects along with s 165 page learn-
ing and theory manual. The PL300 walks you through
the learning phase of digital electronics. If you're
looking for the ultimate lab kit, check out our PL500.
It includes a whopping 500 separate projects, a 152
page starter course manual, a 78 page advanced
course manual, and a 140 page programming course
manual! The PL500 covers everything from the basics
to digital programming!

If you are looking to either learn or hone up on your
through hole or SMT soldering skills check our SP1A
and SM200K Practical Soldering Labs. You will be a
soldering master in no time!

We make it easy to learn IC’s while at the same time,
building a neat AM/FM radio with our AMFM108K
AM/FM IC lab kit. You will have a blast AND learn!

PL130A 130-In-One Lab Kit $39.95
PL200 200-In-One Lab Kit $84.95
PL300 300-In-One Lab Kit $109.95
PL500 500-In-One Lab Kit $249.95
SPIA Through Hold Soldering Lab $9.95
SM200K _ SMT Practical Soldering Lab $22.95
AMFM108K AM/FM IC Lab Kit & Course $36.95 /

RAMSEY ELECTRONICS®
590 Fishers Station Drive
Victor, NY 14564

www.ramseykits.com

Prices, availability, and specifications are subject to change. We are not responsible for typos, stupids, printer's bleed, or
confusion that April showers bring May flowers! Robin thinks winter is over, just because she lives in CA! Wrong!
Visit www.ramseykits.com for the latest pricing, specials, terms and conditions. Copyright 2015 Ramsey Electronics®... so there!

NVRMZ142 and receive 10% off (800) 446-2295

(585) 924-4560

your order!

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